Laser BasicsA laser creates, amplifies and transmits a narrow, concentrated beam of light. Laser is an acronym for light amplification by stimulated emission of radiation.

SOURCES: How Stuff Works, The Learning Co. Inc., Encyclopedia.com and staff reporting | The Washington Post

http://www.washingtonpost.com/wp-srv/metro/daily/graphics/laser_012705.html

http://www.hk-phy.org/articles/laser/laser_e.html

The term laser should not sound alien to you. We often encounter laser in our daily life, examples include the laser pointer used in classrooms, and the CD-ROMs in a computer or in a hi-fi that are used to read the data stored in a CD. In industry, laser is often used for cutting and microscopic processing. For military purposes, laser is used to intercept guided missiles. Scientists have also accurately measured the distance between the Earth and the Moon by using laser; the error involved is only a few centimetres. These are some extensive applications of laser. So actually how is it produced? We will explain the basic principles of laser below. 

It took a very long time to develop laser. Renowned physicist Einstein has already discovered its principles in 1917, but it was not until 1958 that laser was successfully produced. 

Laser is an acronym of Light Amplification by the Stimulated Emission of Radiation. The full name itself exhibits the major processes involved in laser production. Before we look into these processes, we must, first of all, understand the structure of matter, and the principles of light emission and absorption. 

Matter is made up of atoms. Fig. 1 shows a schematic diagram of a carbon atom. At the centre of the atom lies the nucleus; it is constituted of protons and neutrons. A proton carries a positive charge but a neutron does not carry any charge. Outside the atom is a cloud of electrons that carry negative charges; they are in motion surrounding the nucleus. An interesting point to note is that in an atom the energy of an electron is not arbitrary. By quantum mechanics, which describes the microscopic world, each electron stay at a certain energy level, and different energy levels correspond to different energies of the electrons. To simplify the picture, we could imagine the energy levels as some orbits surrounding the nucleus; the farther away they are from the nucleus, the higher their energy would be, as shown in Fig. 1. Moreover, the maximum number of electrons that each orbit can accommodate differs as well. For example, the lowest orbit (the one closest to the nucleus) has a capacity of two electrons, while the higher orbit can hold at most eight. This simplified model is actually not entirely accurate [1], but it can sufficiently help us to explain the basic principles of laser. 

Electrons can transit to other energy levels by absorbing or releasing energy. For example, after an electron has absorbed a photon [2], it transits from a lower energy level to a higher one (Fig. 2a). By the same token, an electron at a higher energy level may transit to a lower one if it releases a photon (Fig. 2b). In these processes, the energy of the photon absorbed or released always equals the energy difference between the two levels. Since the energy of the photon governs the wavelength of light, the absorbed or emitted light has a definite colour. 

Fig. 2  Electron transitions in an atom.

When all electrons of an atom are at the lowest possible energy levels and thus the atom possesses the lowest energy it has, we say that it is at the ground state. Fig. 1 shows the electronic configuration of a carbon atom at the ground state. When one or more electrons are at a higher energy level, we say that the atom is at an excited state. It is mentioned earlier that electrons transit between energy levels by absorbing or emitting light. These transitions are divided into three types:

Fig. 1   Schematic diagram of a carbon atom.

1. Spontaneous absorption - an electron transit from a lower energy level to a higher one by absorbing a photon (Fig. 2a)

2. Spontaneous emission - an electron spontaneously emits a photon to transit from a higher energy level to a lower one (Fig. 2b)

3. Stimulated emission - photons incident into the matter to stimulate the electrons to transit from a higher energy level to a lower one and to emit a photon. The incident photon and their emitted counterparts have the same wavelength and phase; this wavelength corresponds to the energy difference between the two energy levels. A photon stimulates an atom to emit another photon, and hence two identical photons are resulted (Fig. 2c)

Laser is basically produced by the third transition mechanism. The principles of ruby laser are shown in Fig. 3. It comprises a flash lamp, a laser medium and two mirrors. The laser medium is a ruby crystal containing a slight amount of chromium atoms. At start, the flash lamp injects light into the laser medium, stimulating the chromium atoms in it and exciting the electrons at the outermost layer of the atoms. At this moment, some electrons will return to a lower energy level by emitting photons. The emitted photons will be reflected by the mirrors set at the two ends of the laser medium to stimulate more electrons to undergo stimulated emissions, thus increasing the intensity of the laser. One of the mirrors at the two ends will reflect all the photons while the other will reflect most of them, and the remaining small portion of photons that passes through the latter mirror constitute the laser we see. 

There is another feat involved in producing laser: to reach the state of the so-called population inversion. Take the ruby laser as an example (Fig. 4). An atom firstly absorbs energy and transits to an excited state. The atom stays at the excited state only momentarily:

after   seconds, it falls to an intermediate state called metastable state. It stays at the

metastable state for a rather long time: around   seconds or more. Its prolonged stay at the metastable state causes the number of atoms at the state being larger than that at the ground state, and such a phenomenon is called population inversion. Population inversion is a key to producing laser, because it ensures that the number of atoms returning from the metastable state to the ground state by stimulated emission is more than that transiting from the ground state to the metastable state by spontaneous absorption, so that the number of photons in the medium will increase and hence there is a laser output. 

The laser produced from stimulated emission has the following three major characteristics (Fig. 5):

1. It is monochromatic. Only light of a single wavelength is produced in the whole process. This differs from ordinary light such as sunshine or lamplight, which are composed of different wavelengths of light, being close to white light.

2. It is coherent. All photons have the same phase and the same polarization, hence they produce an very high intensity when they superpose. The lights we see in daily life have random phases and polarization, and hence they are relatively much weaker.

Fig. 3  Schematic diagram of a ruby laser.

Fig. 4  Population inversion is key to producing laser.

Fig. 5  Comparing laser and ordinary lamplight.

3. It has a very narrow and collimated ray, and hence it is very powerful. In contrast, lamplight diverges towards different directions and has a low intensity.

Based on its power, laser can be divided into three types, the first being low power laser which uses gas as its laser medium. For example, the barcode scanner often used in supermarkets utilizes helium gas and neon gas as its laser medium. The second type is medium power laser, such as the laser pointers used in classrooms. The last type is high power laser which uses semiconductors as laser medium. Its power output can reach 500 mW. The laser used in the thermonuclear fusion experiments can emit momentary but

extremely intense laser pulses whose pulsation power reaches   W! Such laser could produce a high temperature of a hundred million degrees Celsius and stimulate the deuterium-tritium particle fuels to undergo thermonuclear fusion. 

[1] According to quantum physics, electrons do not move on definite orbits surrounding the nucleus, the position of the electrons is predictable only in a probabilistic way by using the Schrodinger equation.[2] Quantum physics shows that light possesses the properties of particle, especially when it is interacting with an atom. The particles of light are called photons.

LaserFrom Wikipedia, the free encyclopedia

For other uses, see Laser (disambiguation).

United States Air Force laser experiment

Red (635 nm), green (532 nm), and blue-violet (445 nm) lasers

Laser adalah alat yang memancarkan cahaya (radiasi elektromagnetik) melalui proses amplifikasi optik

berdasarkan emisi terstimulasi foton. Istilah "laser" berasal sebagai singkatan dari Light Amplifikasi oleh

Merangsang Emisi Radiasi [1] [2]. Lampu laser yang dipancarkan adalah penting untuk tingkat tinggi

koherensi ruang dan waktu, tak terjangkau menggunakan teknologi lainnya.

Koherensi spasial biasanya diekspresikan melalui output menjadi sinar sempit yang difraksi terbatas,

sering disebut "sinar pensil." Sinar laser dapat difokuskan ke tempat-tempat yang sangat kecil, mencapai

radiasi sangat tinggi. Atau mereka dapat diluncurkan menjadi sinar dari perbedaan yang sangat rendah

dalam rangka untuk berkonsentrasi kekuasaan mereka pada jarak yang besar.

Temporal (atau longitudinal) koherensi menyiratkan gelombang terpolarisasi pada satu frekuensi yang fase

berkorelasi melalui jarak yang relatif besar (panjang koherensi) bersama balok [3] Sebuah sinar yang

dihasilkan oleh sumber cahaya termal atau lainnya tidak koheren. Memiliki amplitudo sesaat dan fase yang

bervariasi secara acak terhadap waktu dan posisi, dan dengan demikian panjang koherensi yang sangat

singkat.

Sebagian besar apa yang disebut "panjang gelombang tunggal" laser benar-benar menghasilkan radiasi

dalam beberapa mode yang memiliki frekuensi sedikit berbeda (panjang gelombang), sering tidak dalam

polarisasi tunggal. Dan meskipun koherensi temporal menyiratkan monochromaticity, bahkan ada laser

yang memancarkan spektrum yang luas cahaya atau memancarkan panjang gelombang cahaya yang

berbeda secara bersamaan. Ada beberapa laser yang tidak modus spasial tunggal dan akibatnya sinar

cahaya mereka menyimpang lebih dari yang dibutuhkan oleh batas difraksi. Namun semua perangkat

tersebut diklasifikasikan sebagai "laser" berdasarkan metode mereka menghasilkan cahaya bahwa: emisi

terstimulasi. Laser bekerja di aplikasi di mana cahaya dari koherensi spasial atau temporal yang diperlukan

tidak dapat diproduksi dengan menggunakan teknologi sederhana.

Terminology

Laser beams in fog, reflected on a car windshield

The word laser started as an acronym for "light amplification by stimulated emission of radiation"; in

modern usage "light" broadly denotes electromagnetic radiation of any frequency, not only visible light,

hence infrared laser, ultraviolet laser, X-ray laser, and so on. Because the microwave predecessor of the

laser, the maser, was developed first, devices of this sort operating at microwave and radio frequencies are

referred to as "masers" rather than "microwave lasers" or "radio lasers". In the early technical literature,

especially at Bell Telephone Laboratories, the laser was called anoptical maser; this term is now obsolete.

[4]

A laser which produces light by itself is technically an optical oscillator rather than an optical amplifier as

suggested by the acronym. It has been humorously noted that the acronym LOSER, for "light oscillation by

stimulated emission of radiation," would have been more correct.[5] With the widespread use of the original

acronym as a common noun, actual optical amplifiers have come to be referred to as "laser amplifiers",

notwithstanding the apparent redundancy in that designation.

The back-formed verb to lase is frequently used in the field, meaning "to produce laser light,"[6] especially in

reference to the gain medium of a laser; when a laser is operating it is said to be "lasing." Further use of

the words laser and maser in an extended sense, not referring to laser technology or devices, can be seen

in usages such as astrophysical maser and atom laser.

Design

Components of a typical laser:

1. Gain medium

2. Laser pumping energy

3. High reflector

4. Output coupler

5. Laser beam

Main article: Laser construction

A laser consists of a gain medium, a mechanism to supply energy to it, and something to provide

optical feedback.[7] The gain medium is a material with properties that allow it to amplify light by stimulated

emission. Light of a specific wavelength that passes through the gain medium is amplified (increases in

power).

For the gain medium to amplify light, it needs to be supplied with energy. This process is called pumping.

The energy is typically supplied as an electrical current, or as light at a different wavelength. Pump light

may be provided by a flash lamp or by another laser.

The most common type of laser uses feedback from an optical cavity—a pair of mirrors on either end of the

gain medium. Light bounces back and forth between the mirrors, passing through the gain medium and

being amplified each time. Typically one of the two mirrors, the output coupler, is partially transparent.

Some of the light escapes through this mirror. Depending on the design of the cavity (whether the mirrors

are flat or curved), the light coming out of the laser may spread out or form a narrow beam. This type of

device is sometimes called a laser oscillator in analogy to electronic oscillators, in which an electronic

amplifier receives electrical feedback that causes it to produce a signal.

Most practical lasers contain additional elements that affect properties of the emitted light such as the

polarization, the wavelength, and the shape of the beam.

Laser physics

See also: Laser science

Electrons and how they interact with electromagnetic fields are important in our understanding

of chemistry and physics.

Stimulated emission

In the classical view, the energy of an electron orbiting an atomic nucleus is larger for orbits further from

the nucleus of an atom. However, quantum mechanical effects force electrons to take on discrete positions

in orbitals. Thus, electrons are found in specific energy levels of an atom, two of which are shown below:

When an electron absorbs energy either from light (photons) or heat (phonons), it receives that incident

quanta of energy. But transitions are only allowed in between discrete energy levels such as the two shown

above. This leads to emission lines and absorption lines.

When an electron is excited from a lower to a higher energy level, it will not stay that way forever. An

electron in an excited state may decay to a lower energy state which is not occupied, according to a

particular time constant characterizing that transition. When such an electron decays without external

influence, emitting a photon, that is called "spontaneous emission". The phase associated with the photon

that is emitted is random. A material with many atoms in such an excited state may thus result

in radiation which is very spectrally limited (centered around one wavelength of light), but the individual

photons would have no common phase relationship and would emanate in random directions. This is the

mechanism of fluorescence and thermal emission.

An external electromagnetic field at a frequency associated with a transition can affect the quantum

mechanical state of the atom. As the electron in the atom makes a transition between two stationary states

(neither of which shows a dipole field), it enters a transition state which does have a dipole field, and which

acts like a small electric dipole, and this dipole oscillates at a characteristic frequency. In response to the

external electric field at this frequency, the probability of the atom entering this transition state is greatly

increased. Thus, the rate of transitions between two stationary states is enhanced beyond that due to

spontaneous emission. Such a transition to the higher state is called absorption, and it destroys an incident

photon (the photon's energy goes into powering the increased energy of the higher state). A transition from

the higher to a lower energy state, however, produces an additional photon; this is the process

ofstimulated emission.

Gain medium and cavity

A helium-neon laser demonstration at the Kastler-Brossel Laboratory at Univ. Paris 6. The pink-orange glow running through the center of the tube is from

the electric discharge which produces incoherent light, just as in a neon tube. This glowing plasma is excited and then acts as the gain mediumthrough which

the internal beam passes, as it is reflected between the two mirrors. Laser radiation output through the front mirror can be seen to produce a tiny (about 1mm

in diameter) intense spot on the screen, to the right. Although it is a deep and pure red color, spots of laser light are so intense that cameras are typically

overexposed and distort their color.

Spectrum of a helium neon laser illustrating its very high spectral purity (limited by the measuring apparatus). The .002 nm bandwidth of the lasing medium is

well over 10,000 times narrower than the spectral width of a light-emitting diode (whose spectrum is shown here for comparison), with the bandwidth of a

single longitudinal mode being much narrower still.

The gain medium is excited by an external source of energy into an excited state. In most lasers this

medium consists of population of atoms which have been excited into such a state by means of an outside

light source, or a electrical field which supplies energy for atoms to absorb and be transformed into their

excited states.

The gain medium of a laser is normally a material of controlled purity, size, concentration, and shape,

which amplifies the beam by the process of stimulated emission described above. This material can be of

any state: gas, liquid, solid, or plasma. The gain medium absorbs pump energy, which raises some

electrons into higher-energy ("excited") quantum states. Particles can interact with light by either absorbing

or emitting photons. Emission can be spontaneous or stimulated. In the latter case, the photon is emitted in

the same direction as the light that is passing by. When the number of particles in one excited state

exceeds the number of particles in some lower-energy state, population inversion is achieved and the

amount of stimulated emission due to light that passes through is larger than the amount of absorption.

Hence, the light is amplified. By itself, this makes an optical amplifier. When an optical amplifier is placed

inside a resonant optical cavity, one obtains a laser oscillator.[8]

In a few situations it is possible to obtain lasing with only a single pass of EM radiation through the gain

medium, and this produces a laser beam without any need for a resonant or reflective cavity (see for

example nitrogen laser).[9] Thus, reflection in a resonant cavity is usually required for a laser, but is not

absolutely necessary.

The optical resonator is sometimes referred to as an "optical cavity", but this is a misnomer: lasers use

open resonators as opposed to the literal cavity that would be employed at microwave frequencies in

a maser. The resonator typically consists of two mirrors between which a coherent beam of light travels in

both directions, reflecting back on itself so that an average photon will pass through the gain medium

repeatedly before it is emitted from the output aperture or lost to diffraction or absorption. If the gain

(amplification) in the medium is larger than the resonator losses, then the power of the recirculating light

can rise exponentially. But each stimulated emission event returns an atom from its excited state to the

ground state, reducing the gain of the medium. With increasing beam power the net gain (gain times loss)

reduces to unity and the gain medium is said to be saturated. In a continuous wave (CW) laser, the balance

of pump power against gain saturation and cavity losses produces an equilibrium value of the laser power

inside the cavity; this equilibrium determines the operating point of the laser. If the applied pump power is

too small, the gain will never be sufficient to overcome the resonator losses, and laser light will not be

produced. The minimum pump power needed to begin laser action is called the lasing threshold. The gain

medium will amplify any photons passing through it, regardless of direction; but only the photons in

a spatial modesupported by the resonator will pass more than once through the medium and receive

substantial amplification.

The light emitted

The light generated by stimulated emission is very similar to the input signal in terms of wavelength, phase,

and polarization. This gives laser light its characteristic coherence, and allows it to maintain the uniform

polarization and often monochromaticity established by the optical cavity design.

The beam in the cavity and the output beam of the laser, when travelling in free space (or a homogenous

medium) rather than waveguides (as in anoptical fiber laser), can be approximated as a Gaussian beam in

most lasers; such beams exhibit the minimum divergence for a given diameter. However some high power

lasers may be multimode, with the transverse modes often approximated using Hermite-

Gaussian or Laguerre-Gaussian functions. It has been shown that unstable laser resonators (not used in

most lasers) produce fractal shaped beams.[10] Near the beam "waist" (or focal region) it is

highly collimated: the wavefronts are planar, normal to the direction of propagation, with no beam

divergence at that point. However due todiffraction, that can only remain true well within the Rayleigh

range. The beam of a single transverse mode (gaussian beam) laser eventually diverges at an angle which

varies inversely with the beam diameter, as required by diffraction theory. Thus, the "pencil beam" directly

generated by a commonhelium-neon laser would spread out to a size of perhaps 500 kilometers when

shone on the Moon (from the distance of the earth). On the other hand the light from a semiconductor

laser typically exits the tiny crystal with a large divergence: up to 50°. However even such a divergent beam

can be transformed into a similarly collimated beam by means of a lens system, as is always included, for

instance, in a laser pointer whose light originates from a laser diode. That is possible due to the light being

of a single spatial mode. This unique property of laser light, spatial coherence, cannot be replicated using

standard light sources (except by discarding most of the light) as can be appreciated by comparing the

beam from a flashlight (torch) or spotlight to that of almost any laser.

Quantum vs. classical emission processes

The mechanism of producing radiation in a laser relies on stimulated emission, where energy is extracted

from a transition in an atom or molecule. This is a quantum phenomenon discovered byEinstein who

derived the relationship between the A coefficient describing spontaneous emission and the B

coefficient which applies to absorption and stimulated emission. However in the case of the free electron

laser, atomic energy levels are not involved; it appears that the operation of this rather exotic device can be

explained without reference to quantum mechanics.

Continuous and pulsed modes of operation

A laser can be classified as operating in either continuous or pulsed mode, depending on whether the

power output is essentially continuous over time or whether its output takes the form of pulses of light on

one or another time scale. Of course even a laser whose output is normally continuous can be intentionally

turned on and off at some rate in order to create pulses of light. When the modulation rate is on time scales

much slower than the cavity lifetime and the time period over which energy can be stored in the lasing

medium or pumping mechanism, then it is still classified as a "modulated" or "pulsed" continuous wave

laser. Most laser diodes used in communication systems fall in that category.

Continuous wave operation

Some applications of lasers depend on a beam whose output power is constant over time. Such a laser is

known as continuous wave (CW). Many types of lasers can be made to operate in continuous wave mode

to satisfy such an application. Many of these lasers actually lase in several longitudinal modes at the same

time, and beats between the slightly different optical frequencies of those oscillations will in fact produce

amplitude variations on time scales shorter than the round-trip time (the reciprocal of the frequency

spacing between modes), typically a few nanoseconds or less. In most cases these lasers are still termed

"continuous wave" as their output power is steady when averaged over any longer time periods, with the

very high frequency power variations having little or no impact in the intended application. (However the

term is not applied to mode-locked lasers, where the intention is to create very short pulses at the rate of

the round-trip time).

For continuous wave operation it is required for the population inversion of the gain medium to be

continually replenished by a steady pump source. In some lasing media this is impossible. In some other

lasers it would require pumping the laser at a very high continuous power level which would be impractical

or destroy the laser by producing excessive heat. Such lasers cannot be run in CW mode.

Pulsed operation

Pulsed operation of lasers refers to any laser not classified as continuous wave, so that the optical power

appears in pulses of some duration at some repetition rate. This encompasses a wide range of

technologies addressing a number of different motivations. Some lasers are pulsed simply because they

cannot be run in continuous mode.

In other cases the application requires the production of pulses having as large an energy as possible.

Since the pulse energy is equal to the average power divided by the repetition rate, this goal can

sometimes be satisfied by lowering the rate of pulses so that more energy can be built up in between

pulses. In laser ablation for example, a small volume of material at the surface of a work piece can be

evaporated if it is heated in a very short time, whereas supplying the energy gradually would allow for the

heat to be absorbed into the bulk of the piece, never attaining a sufficiently high temperature at a particular

point.

Other applications rely on the peak pulse power (rather than the energy in the pulse), especially in order to

obtain nonlinear optical effects. For a given pulse energy, this requires creating pulses of the shortest

possible duration utilizing techniques such as Q-switching.

The optical bandwidth of a pulse cannot be narrower than the reciprocal of the pulse width. In the case of

extremely short pulses, that implies lasing over a considerable bandwidth, quite contrary to the very narrow

bandwidths typical of CW lasers. The lasing medium in some dye lasers and vibronic solid-state

lasers produces optical gain over a wide bandwidth, making a laser possible which can thus generate

pulses of light as short as a few femtoseconds (10−15 s).

Q-switching

Main article: Q-switching

In a Q-switched laser, the population inversion is allowed to build up by introducing loss inside the

resonator which exceeds the gain of the medium; this can also be described as a reduction of the quality

factor or 'Q' of the cavity. Then, after the pump energy stored in the laser medium has approached the

maximum possible level, the introduced loss mechanism (often an electro- or acousto-optical element) is

rapidly removed (or that occurs by itself in a passive device), allowing lasing to begin which rapidly obtains

the stored energy in the gain medium. This results in a short pulse incorporating that energy, and thus a

high peak power.

Mode-locking

Main article: Mode-locking

A mode-locked laser is capable of emitting extremely short pulses on the order of tens

of picoseconds down to less than 10 femtoseconds. These pulses will repeat at the round trip time, that is,

the time that it takes light to complete one round trip between the mirrors comprising the resonator. Due to

the Fourier limit (also known as energy-time uncertainty), a pulse of such short temporal length has a

spectrum spread over a considerable bandwidth. Thus such a gain medium must have a gain bandwidth

sufficiently broad to amplify those frequencies. An example of a suitable material is titanium-doped,

artificially grown sapphire (Ti:sapphire) which has a very wide gain bandwidth and can thus produce pulses

of only a few femtoseconds duration.

Such mode-locked lasers are a most versatile tool for researching processes occurring on extremely short

time scales (known as femtosecond physics, femtosecond chemistry and ultrafast science), for maximizing

the effect of nonlinearity in optical materials (e.g. in second-harmonic generation, parametric down-

conversion, optical parametric oscillators and the like) due to the large peak power, and in ablation

applications.[citation needed] Again, because of the extremely short pulse duration, such a laser will produce

pulses which achieve an extremely high peak power.

Pulsed pumping

Another method of achieving pulsed laser operation is to pump the laser material with a source that is itself

pulsed, either through electronic charging in the case of flash lamps, or another laser which is already

pulsed. Pulsed pumping was historically used with dye lasers where the inverted population lifetime of a

dye molecule was so short that a high energy, fast pump was needed. The way to overcome this problem

was to charge up large capacitors which are then switched to discharge through flashlamps, producing an

intense flash. Pulsed pumping is also required for three-level lasers in which the lower energy level rapidly

becomes highly populated preventing further lasing until those atoms relax to the ground state. These

lasers, such as the excimer laser and the copper vapor laser, can never be operated in CW mode.

History

Foundations

In 1917, Albert Einstein established the theoretic foundations for the laser and the maser in the paper Zur

Quantentheorie der Strahlung (On the Quantum Theory of Radiation); via a re-derivation of Max Planck’s

law of radiation, conceptually based upon probability coefficients (Einstein coefficients) for the absorption,

spontaneous emission, and stimulated emission of electromagnetic radiation; in 1928, Rudolf W.

Ladenburg confirmed the existences of the phenomena of stimulated emission and negative absorption;

[11] in 1939, Valentin A. Fabrikant predicted the use of stimulated emission to amplify “short” waves;[12] in

1947, Willis E. Lamb and R. C. Retherford found apparent stimulated emission in hydrogen spectra and

effected the first demonstration of stimulated emission;[11] in 1950, Alfred Kastler (Nobel Prize for Physics

1966) proposed the method of optical pumping, experimentally confirmed, two years later, by Brossel,

Kastler, and Winter.[13]

Maser

Main article: Maser

Aleksandr Prokhorov

In 1953, Charles Hard Townes and graduate students James P. Gordon and Herbert J. Zeiger produced

the first microwave amplifier, a device operating on similar principles to the laser, but

amplifying microwave radiation rather than infrared or visible radiation. Townes's maser was incapable of

continuous output.[citation needed] Meanwhile, in the Soviet Union, Nikolay Basov and Aleksandr Prokhorov were

independently working on the quantum oscillator and solved the problem of continuous-output systems by

using more than two energy levels. These gain media could release stimulated emissions between an

excited state and a lower excited state, not the ground state, facilitating the maintenance of a population

inversion. In 1955, Prokhorov and Basov suggested optical pumping of a multi-level system as a method

for obtaining the population inversion, later a main method of laser pumping.

Townes reports that several eminent physicists — among them Niels Bohr, John von Neumann, Isidor

Rabi, Polykarp Kusch, and Llewellyn Thomas — argued the maser violated Heisenberg's uncertainty

principle and hence could not work.[1] In 1964 Charles H. Townes, Nikolay Basov, and Aleksandr

Prokhorov shared the Nobel Prize in Physics, “for fundamental work in the field of quantum electronics,

which has led to the construction of oscillators and amplifiers based on the maser–laser principle”.

Laser

In 1957, Charles Hard Townes and Arthur Leonard Schawlow, then at Bell Labs, began a serious study of

the infrared laser. As ideas developed, they abandoned infrared radiation to instead concentrate

upon visible light. The concept originally was called an "optical maser". In 1958, Bell Labs filed

a patentapplication for their proposed optical maser; and Schawlow and Townes submitted a manuscript of

their theoretical calculations to the Physical Review, published that year in Volume 112, Issue No. 6.

LASER notebook: First page of the notebook wherein Gordon Gould coined the LASER acronym, and described thetechnologic elements for constructing

the device.

Simultaneously, at Columbia University, graduate student Gordon Gould was working on a doctoral

thesis about the energy levels of excited thallium. When Gould and Townes met, they spoke of

radiation emission, as a general subject; afterwards, in November 1957, Gould noted his ideas for a “laser”,

including using an open resonator (later an essential laser-device component). Moreover, in 1958,

Prokhorov independently proposed using an open resonator, the first published appearance (the USSR) of

this idea. Elsewhere, in the U.S., Schawlow and Townes had agreed to an open-resonator laser design —

apparently unaware of Prokhorov’s publications and Gould’s unpublished laser work.

At a conference in 1959, Gordon Gould published the term LASER in the paper The LASER, Light

Amplification by Stimulated Emission of Radiation.[1][5] Gould’s linguistic intention was using the “-aser” word

particle as a suffix — to accurately denote the spectrum of the light emitted by the LASER device; thus x-

rays: xaser, ultraviolet: uvaser, et cetera; none established itself as a discrete term, although “raser” was

briefly popular for denoting radio-frequency-emitting devices.

Gould’s notes included possible applications for a laser, such as spectrometry, interferometry, radar,

and nuclear fusion. He continued developing the idea, and filed a patent application in April 1959. The U.S.

Patent Office denied his application, and awarded a patent to Bell Labs, in 1960. That provoked a twenty-

eight-year lawsuit, featuring scientific prestige and money as the stakes. Gould won his first minor patent in

1977, yet it was not until 1987 that he won the first significant patent lawsuit victory, when a Federal judge

ordered the U.S. Patent Office to issue patents to Gould for the optically pumped and the gas

discharge laser devices. The question of just how to assign credit for inventing the laser remains

unresolved by historians.[14]

On May 16, 1960, Theodore H. Maiman operated the first functioning laser,[15][16] at Hughes Research

Laboratories, Malibu, California, ahead of several research teams, including those of Townes, at Columbia

University, Arthur Schawlow, at Bell Labs,[17] and Gould, at the TRG (Technical Research Group) company.

Maiman’s functional laser used a solid-state flashlamp-pumped synthetic ruby crystal to produce red laser

light, at 694 nanometres wavelength; however, the device only was capable of pulsed operation, because

of its three-level pumping design scheme. Later in 1960, the Iranianphysicist Ali Javan, and William R.

Bennett, and Donald Herriott, constructed the first gas laser, using helium and neon that was capable of

continuous operation in the infrared (U.S. Patent 3,149,290); later, Javan received the Albert Einstein

Award in 1993. Basov and Javan proposed the semiconductorlaser diode concept. In 1962, Robert N.

Hall demonstrated the first laser diode device, made of gallium arsenide and emitted at 850 nm the near-

infrared band of the spectrum. Later, in 1962, Nick Holonyak, Jr. demonstrated the first semiconductor

laser with a visible emission. This first semiconductor laser could only be used in pulsed-beam operation,

and when cooled to liquid nitrogentemperatures (77 K). In 1970, Zhores Alferov, in the USSR, and Izuo

Hayashi and Morton Panish of Bell Telephone Laboratories also independently developed room-

temperature, continual-operation diode lasers, using the heterojunction structure.

Recent innovations

Graph showing the history of maximum laser pulse intensity throughout the past 40 years.

Since the early period of laser history, laser research has produced a variety of improved and specialized

laser types, optimized for different performance goals, including:

new wavelength bands

maximum average output power

maximum peak pulse energy

maximum peak pulse power

minimum output pulse duration

maximum power efficiency

minimum cost

and this research continues to this day.

Lasing without maintaining the medium excited into a population inversion[dubious – discuss] was discovered in

1992 in sodium gas and again in 1995 in rubidium gas by various international teams.[citation needed] This was

accomplished by using an external maser to induce "optical transparency" in the medium by introducing

and destructively interfering the ground electron transitions between two paths, so that the likelihood for the

ground electrons to absorb any energy has been cancelled.

Types and operating principles

For a more complete list of laser types see this list of laser types.

Wavelengths of commercially available lasers. Laser types with distinct laser lines are shown above the wavelength bar, while below are shown

lasers that can emit in a wavelength range. The color codifies the type of laser material (see the figure description for more details).

Gas lasers

Main article: Gas laser

Following the invention of the HeNe gas laser, many other gas discharges have been found to amplify

light coherently. Gas lasers using many different gases have been built and used for many purposes.

The helium-neon laser (HeNe) is able to operate at a number of different wavelengths, however the

vast majority are engineered to lase at 633 nm; these relatively low cost but highly coherent lasers are

extremely common in optical research and educational laboratories. Commercial carbon dioxide (CO2)

lasers can emit many hundreds of watts in a single spatial mode which can be concentrated into a tiny

spot. This emission is in the thermal infrared at 10.6 µm; such lasers are regularly used in industry for

cutting and welding. The efficiency of a CO2 laser is unusually high: over 10%. Argon-ion lasers can

operate at a number of lasing transitions between 351 and 528.7 nm. Depending on the optical design

one or more of these transitions can be lasing simultaneously; the most commonly used lines are

458 nm, 488 nm and 514.5 nm. A nitrogentransverse electrical discharge in gas at atmospheric

pressure (TEA) laser is an inexpensive gas laser, often home-built by hobbyists, which produces rather

incoherent UV light at 337.1 nm.[18] Metal ion lasers are gas lasers that generatedeep

ultraviolet wavelengths. Helium-silver (HeAg) 224 nm and neon-copper (NeCu) 248 nm are two

examples. Like all low-pressure gas lasers, the gain media of these lasers have quite narrow

oscillation linewidths, less than 3 GHz (0.5picometers),[19] making them candidates for use

in fluorescence suppressed Raman spectroscopy.

Chemical lasers

Chemical lasers are powered by a chemical reaction permitting a large amount of energy to be

released quickly. Such very high power lasers are especially of interest to the military, however

continuous wave chemical lasers at very high power levels, fed by streams of gasses, have been

developed and have some industrial applications. As examples, in the Hydrogen fluoride laser(2700-

2900 nm) and the Deuterium fluoride laser (3800 nm) the reaction is the combination of hydrogen or

deuterium gas with combustion products of ethylene in nitrogen trifluoride.

Excimer lasers

Excimer lasers are a special sort of gas laser powered by an electric discharge in which the lasing

medium is an excimer, or more precisely an exciplex in existing designs. These are molecules which

can only exist with one atom in an excited electronic state. Once the molecule transfers its excitation

energy to a photon, therefore, its atoms are no longer bound to each other and the molecule

disintegrates. This drastically reduces the population of the lower energy state thus greatly facilitating a

population inversion. Excimers currently used are all noble gas compounds; noble gasses are

chemically inert and can only form compounds while in an excited state. Excimer lasers typically

operate at ultraviolet wavelengths with major applicatons including

semiconductor photolithography and LASIK eye surgery. Commonly used excimer molecules include

ArF (emission at 193 nm), KrCl (222 nm), KrF (248 nm), XeCl (308 nm), and XeF (351 nm).[20] The

molecular fluorine laser, emitting at 157 nm in the vacuum ultraviolet is sometimes referred to as an

excimer laser, however this appears to be a misnomer inasmuch as F2 is a stable compound.

Solid-state lasers

A frequency-doubled green laser pointer, showing internal construction. Two AAA cells and electronics power the laser module (lower diagram)

This contains a powerful 808 nm IR diode laser that optically pumps a Nd:YVO4 crystal inside a laser cavity. That laser produces 1064 nm

(infrared) light which is mainly confined inside the resonator. Also inside the laser cavity, however, is a non-linear KTP crystal which causes

frequency doubling, resulting in green light at 532 nm. The front mirror is transparent to this visible wavelength which is then expanded and

collimated using two lenses (in this particular design).

Solid-state lasers use a crystalline or glass rod which is "doped" with ions that provide the required

energy states. For example, the first working laser was a ruby laser, made from ruby (chromium-

doped corundum). The population inversion is actually maintained in the "dopant", such

as chromium orneodymium. These materials are pumped optically using a shorter wavelength than the

lasing wavelength, often from a flashtube or from another laser.

It should be noted that "solid-state" in this sense refers to a crystal or glass, but this usage is distinct

from the designation of "solid-state electronics" in referring to semiconductors. Semiconductor lasers

(laser diodes) are pumped electrically and are thus not referred to as solid-state lasers. The class of

solid-state lasers would, however, properly include fiber lasers in which dopants in the glass lase

under optical pumping. But in practice these are simply referred to as "fiber lasers" with "solid-state"

reserved for lasers using a solid rod of such a material.

Neodymium is a common "dopant" in various solid-state laser crystals, including yttrium

orthovanadate (Nd:YVO4), yttrium lithium fluoride (Nd:YLF) andyttrium aluminium garnet (Nd:YAG). All

these lasers can produce high powers in the infrared spectrum at 1064 nm. They are used for cutting,

welding and marking of metals and other materials, and also in spectroscopy and for pumping dye

lasers.

These lasers are also commonly frequency doubled, tripled or quadrupled, in so-called "diode pumped

solid state" or DPSS lasers. Under second, third, or fourth harmonic generation these produce 532 nm

(green, visible), 355 nm and 266 nm (UV) beams. This is the technology behind the bright laser

pointers particularly at green (532 nm) and other short visible wavelengths.

Ytterbium, holmium, thulium, and erbium are other common "dopants" in solid-state lasers. Ytterbium

is used in crystals such as Yb:YAG, Yb:KGW, Yb:KYW, Yb:SYS, Yb:BOYS, Yb:CaF2, typically

operating around 1020-1050 nm. They are potentially very efficient and high powered due to a small

quantum defect. Extremely high powers in ultrashort pulses can be achieved with Yb:YAG. Holmium-

doped YAG crystals emit at 2097 nm and form an efficient laser operating at infrared wavelengths

strongly absorbed by water-bearing tissues. The Ho-YAG is usually operated in a pulsed mode, and

passed through optical fiber surgical devices to resurface joints, remove rot from teeth, vaporize

cancers, and pulverize kidney and gall stones.

Titanium-doped sapphire (Ti:sapphire) produces a highly tunable infrared laser, commonly used

for spectroscopy. It is also notable for use as a mode-locked laser producing ultrashort pulses of

extremely high peak power.

Thermal limitations in solid-state lasers arise from unconverted pump power that manifests itself as

heat. This heat, when coupled with a high thermo-optic coefficient (dn/dT) can give rise to thermal

lensing as well as reduced quantum efficiency. These types of issues can be overcome by another

novel diode-pumped solid-state laser, the diode-pumped thin disk laser. The thermal limitations in this

laser type are mitigated by using a laser medium geometry in which the thickness is much smaller than

the diameter of the pump beam. This allows for a more even thermal gradient in the material. Thin disk

lasers have been shown to produce up to kilowatt levels of power.[21]

Fiber lasers

Main article: Fiber laser

Solid-state lasers or laser amplifiers where the light is guided due to the total internal reflection in a

single mode optical fiber are instead called fiber lasers. Guiding of light allows extremely long gain

regions providing good cooling conditions; fibers have high surface area to volume ratio which allows

efficient cooling. In addition, the fiber's waveguiding properties tend to reduce thermal distortion of the

beam. Erbium and ytterbium ions are common active species in such lasers.

Quite often, the fiber laser is designed as a double-clad fiber. This type of fiber consists of a fiber core,

an inner cladding and an outer cladding. The index of the three concentric layers is chosen so that the

fiber core acts as a single-mode fiber for the laser emission while the outer cladding acts as a highly

multimode core for the pump laser. This lets the pump propagate a large amount of power into and

through the active inner core region, while still having a high numerical aperture (NA) to have easy

launching conditions.

Pump light can be used more efficiently by creating a fiber disk laser, or a stack of such lasers.

Fiber lasers have a fundamental limit in that the intensity of the light in the fiber cannot be so high that

optical nonlinearities induced by the local electric field strength can become dominant and prevent

laser operation and/or lead to the material destruction of the fiber. This effect is called photodarkening.

In bulk laser materials, the cooling is not so efficient, and it is difficult to separate the effects of

photodarkening from the thermal effects, but the experiments in fibers show that the photodarkening

can be attributed to the formation of long-living color centers.[citation needed]

Photonic crystal lasers

Photonic crystal lasers are lasers based on nano-structures that provide the mode confinement and

the density of optical states (DOS) structure required for the feedback to take place.[clarification needed] They

are typical micrometre-sized[dubious – discuss] and tunable on the bands of the photonic crystals.[22][clarification

needed]

Semiconductor lasers

A 5.6 mm 'closed can' commercial laser diode, probably from a CD or DVD player

Semiconductor lasers are diodes which are electrically pumped. Recombination of electrons and holes

created by the applied current introduces optical gain. Reflection from the ends of the crystal form an

optical resonator, although the resonator can be external to the semiconductor in some designs.

Commercial laser diodes emit at wavelengths from 375 nm to 3500 nm. Low to medium power laser

diodes are used in laser printers and CD/DVD players. Laser diodes are also frequently used to

optically pump other lasers with high efficiency. The highest power industrial laser diodes, with power

up to 10 kW (70dBm)[citation needed], are used in industry for cutting and welding. External-cavity

semiconductor lasers have a semiconductor active medium in a larger cavity. These devices can

generate high power outputs with good beam quality, wavelength-tunable narrow-linewidth radiation,

or ultrashort laser pulses.

Vertical cavity surface-emitting lasers (VCSELs) are semiconductor lasers whose emission direction is

perpendicular to the surface of the wafer. VCSEL devices typically have a more circular output beam

than conventional laser diodes, and potentially could be much cheaper to manufacture. As of 2005,

only 850 nm VCSELs are widely available, with 1300 nm VCSELs beginning to be commercialized,

[23] and 1550 nm devices an area of research. VECSELs are external-cavity VCSELs. Quantum

cascade lasers are semiconductor lasers that have an active transition between energysub-bands of

an electron in a structure containing several quantum wells.

The development of a silicon laser is important in the field of optical computing. Silicon is the material

of choice for integrated circuits, and so electronic and silicon photonic components (such asoptical

interconnects) could be fabricated on the same chip. Unfortunately, silicon is a difficult lasing material

to deal with, since it has certain properties which block lasing. However, recently teams have produced

silicon lasers through methods such as fabricating the lasing material from silicon and other

semiconductor materials, such as indium(III) phosphide or gallium(III) arsenide, materials which allow

coherent light to be produced from silicon. These are called hybrid silicon laser. Another type is

a Raman laser, which takes advantage of Raman scattering to produce a laser from materials such as

silicon.

Dye lasers

Dye lasers use an organic dye as the gain medium. The wide gain spectrum of available dyes, or

mixtures of dyes, allows these lasers to be highly tunable, or to produce very short-duration pulses (on

the order of a few femtoseconds). Although these tunable lasers are mainly known in their liquid form,

researchers have also demonstrated narrow-linewidth tunable emission in dispersive oscillator

configurations incorporating solid-state dye gain media.[24] In their most prevalent form these solid state

dye lasers use dye-doped polymers as laser media.

Free electron lasers

Free electron lasers, or FELs, generate coherent, high power radiation, that is widely tunable, currently

ranging in wavelength from microwaves, through terahertz radiation and infrared, to the visible

spectrum, to soft X-rays. They have the widest frequency range of any laser type. While FEL beams

share the same optical traits as other lasers, such as coherent radiation, FEL operation is quite

different. Unlike gas, liquid, or solid-state lasers, which rely on bound atomic or molecular states, FELs

use a relativistic electron beam as the lasing medium, hence the termfree electron.

Bio laser

Living cells can be genetically engineered to produce Green fluorescent protein (GFP). The GFP is

used as the laser's "gain medium", where light amplification takes place. The cells are then placed

between two tiny mirrors, just 20 millionths of a metre across, which acted as the "laser cavity" in

which light could bounce many times through the cell. Upon bathing the cell with blue light, it could be

seen to emit directed and intense green laser light.[25][26]

Exotic laser media

In September 2007, the BBC News reported that there was speculation about the possibility of

using positronium annihilation to drive a very powerful gamma ray laser.[27] Dr. David Cassidy of

theUniversity of California, Riverside proposed that a single such laser could be used to ignite

a nuclear fusion reaction, replacing the banks of hundreds of lasers currently employed in inertial

confinement fusion experiments.[27]

Space-based X-ray lasers pumped by a nuclear explosion have also been proposed as antimissile

weapons.[28][29] Such devices would be one-shot weapons.

Uses

Lasers range in size from microscopicdiode lasers (top) with numerous applications, to football field sizedneodymium glass lasers (bottom) used

forinertial confinement fusion, nuclear weapons research and other high energy density physics experiments.

Main article: List of applications for lasers

When lasers were invented in 1960, they were called "a solution looking for a problem".[30] Since then,

they have become ubiquitous, finding utility in thousands of highly varied applications in every section

of modern society, including consumer electronics, information

technology, science, medicine,industry, law enforcement, entertainment, and the military.

The first use of lasers in the daily lives of the general population was the

supermarket barcode scanner, introduced in 1974. The laserdisc player, introduced in 1978, was the

first successful consumer product to include a laser but the compact disc player was the first laser-

equipped device to become common, beginning in 1982 followed shortly by laser printers.

Some other uses are:

Medicine : Bloodless surgery, laser healing, surgical treatment, kidney stone treatment, eye

treatment, dentistry

Industry : Cutting, welding, material heat treatment, marking parts, non-contact measurement of

parts

Military : Marking targets, guiding munitions, missile defence, electro-optical countermeasures

(EOCM), alternative to radar, blinding troops.

Law enforcement : used for latent fingerprint detection in the forensic identification field[31][32]

Research : Spectroscopy, laser ablation, laser annealing, laser scattering,

laser interferometry, LIDAR, laser capture microdissection, fluorescence microscopy

Product development/commercial: laser printers, optical discs (e.g. CDs and the

like), barcode scanners, thermometers, laser pointers, holograms,bubblegrams.

Laser lighting displays : Laser light shows

Cosmetic  skin treatments: acne treatment, cellulite and striae reduction, and hair removal.

In 2004, excluding diode lasers, approximately 131,000 lasers were sold with a value of US$2.19

billion.[33] In the same year, approximately 733 million diode lasers, valued at $3.20 billion, were sold.[34]

Examples by power

Laser application in astronomical adaptive opticsimaging

Different applications need lasers with different output powers. Lasers that produce a continuous beam

or a series of short pulses can be compared on the basis of their average power. Lasers that produce

pulses can also be characterized based on the peak power of each pulse. The peak power of a pulsed

laser is manyorders of magnitude greater than its average power. The average output power is always

less than the power consumed.

The continuous or average power required for some uses:

Power Use

1-5 mW Laser pointers

5 mW CD-ROM drive

5–10 mW DVD player or DVD-ROM drive

100 mW High-speed CD-RW burner

250 mW Consumer 16x DVD-R burner

400 mWBurning through a jewel case including disk within 4 seconds[35]

DVD 24x dual-layer recording.[36]

1 W Green laser in current Holographic Versatile Disc prototype development

1–20 WOutput of the majority of commercially available solid-state lasers used for micro machining

30–100 W Typical sealed CO2 surgical lasers[37]

100–3000 W

Typical sealed CO2 lasers used in industrial laser cutting

5 kW Output power achieved by a 1 cm diode laser bar[38]

100 kWClaimed output of a CO2 laser being developed by Northrop Grumman for military (weapon) applications

Examples of pulsed systems with high peak power:

700 TW (700×1012 W) – National Ignition Facility, a 192-beam, 1.8-megajoule laser system

adjoining a 10-meter-diameter target chamber.[39]

1.3 PW (1.3×1015 W) – world's most powerful laser as of 1998, located at the Lawrence Livermore

Laboratory [40]

Hobby uses

In recent years, some hobbyists have taken interests in lasers. Lasers used by hobbyists are generally

of class IIIa or IIIb, although some have made their own class IV types.[41] However, compared to other

hobbyists, laser hobbyists are far less common, due to the cost and potential dangers involved. Due to

the cost of lasers, some hobbyists use inexpensive means to obtain lasers, such as salvaging laser

diodes from broken DVD players (red), Blu-ray players (violet), or even higher power laser diodes from

CD or DVD burners.[42]

Hobbyists also have been taking surplus pulsed lasers from retired military applications and modifying

them for pulsed holography. Pulsed Ruby and pulsed YAG lasers have been used.

Safety

Warning symbol for lasers

Laser warning label

Main article: Laser safety

Even the first laser was recognized as being potentially dangerous. Theodore Maiman characterized

the first laser as having a power of one "Gillette" as it could burn through one Gillette razor blade.

Today, it is accepted that even low-power lasers with only a few milliwatts of output power can be

hazardous to human eyesight, when the beam from such a laser hits the eye directly or after reflection

from a shiny surface. At wavelengths which the cornea and the lens can focus well, the coherence and

low divergence of laser light means that it can be focused by the eye into an extremely small spot on

the retina, resulting in localized burning and permanent damage in seconds or even less time.

Lasers are usually labeled with a safety class number, which identifies how dangerous the laser is:

Class I/1 is inherently safe, usually because the light is contained in an enclosure, for example in

CD players.

Class II/2 is safe during normal use; the blink reflex of the eye will prevent damage. Usually up to

1 mW power, for example laser pointers.

Class IIIa/3R lasers are usually up to 5 mW and involve a small risk of eye damage within the time

of the blink reflex. Staring into such a beam for several seconds is likely to cause damage to a

spot on the retina.

Class IIIb/3B can cause immediate eye damage upon exposure.

Class IV/4 lasers can burn skin, and in some cases, even scattered light can cause eye and/or

skin damage. Many industrial and scientific lasers are in this class.

The indicated powers are for visible-light, continuous-wave lasers. For pulsed lasers and invisible

wavelengths, other power limits apply. People working with class 3B and class 4 lasers can protect

their eyes with safety goggles which are designed to absorb light of a particular wavelength.

Certain infrared lasers with wavelengths beyond about 1.4 micrometres are often referred to as being

"eye-safe". This is because the intrinsic molecular vibrations of water molecules very strongly absorb

light in this part of the spectrum, and thus a laser beam at these wavelengths is attenuated so

completely as it passes through the eye's cornea that no light remains to be focused by the lens onto

the retina. The label "eye-safe" can be misleading, however, as it only applies to relatively low power

continuous wave beams; any high power or Q-switched laser at these wavelengths can burn the

cornea, causing severe eye damage.

As weapons

Laser beams are famously employed as weapon systems in science fiction, but actual laser

weapons are still in the experimental stage. The general idea of laser-beam weaponry is to hit a target

with a train of brief pulses of light. The rapid evaporation and expansion of the surface causes

shockwaves[citation needed] that damage the target. The power needed to project a high-powered laser

beam of this kind is beyond the limit of current mobile power technology thus favoring chemically

powered gas dynamic lasers.

Lasers of all but the lowest powers can potentially be used as incapacitating weapons, through their

ability to produce temporary or permanent vision loss in varying degrees when aimed at the eyes. The

degree, character, and duration of vision impairment caused by eye exposure to laser light varies with

the power of the laser, the wavelength(s), the collimation of the beam, the exact orientation of the

beam, and the duration of exposure. Lasers of even a fraction of a watt in power can produce

immediate, permanent vision loss under certain conditions, making such lasers potential non-lethal but

incapacitating weapons. The extreme handicap that laser-induced blindness represents makes the use

of lasers even as non-lethal weapons morally controversial, and weapons designed to cause blindness

have been banned by the Protocol on Blinding Laser Weapons. The U.S. Air Force is currently working

on the Boeing YAL-1 airborne laser, mounted in a Boeing 747, to shoot down enemy ballistic missiles

over enemy territory.

In the field of aviation, the hazards of exposure to ground-based lasers deliberately aimed at pilots

have grown to the extent that aviation authorities have special procedures to deal with such hazards.[43]

On March 18, 2009 Northrop Grumman claimed that its engineers in Redondo Beach had successfully

built and tested an electrically powered solid state laser capable of producing a 100-kilowatt beam,

powerful enough to destroy an airplane. According to Brian Strickland, manager for the United States

Army's Joint High Power Solid State Laser program, an electrically powered laser is capable of being

mounted in an aircraft, ship, or other vehicle because it requires much less space for its supporting

equipment than a chemical laser.[44] However the source of such a large electrical power in a mobile

application remains unclear.

Fictional predictions

See also: Raygun

Several novelists described devices similar to lasers, prior to the discovery of stimulated emission:

A laser-like device was described in Alexey Tolstoy's science fiction novel The Hyperboloid of

Engineer Garin in 1927.

Mikhail Bulgakov  exaggerated the biological effect (laser bio stimulation) of intensive red light in

his science fiction novel Fatal Eggs (1925), without any reasonable description of the source of

this red light. (In that novel, the red light first appears occasionally from the illuminating system of

an advanced microscope; then the protagonist Prof. Persikov arranges the special set-up for

generation of the red light.)

See also

Bessel beam

Coherent perfect absorber

dazzler (weapon)

Free-space optical communication

Homogeneous broadening

Induced gamma emission

Injection seeder

International Laser Display

Association

Laser accelerometer

Lasers and aviation safety

Laser beam profiler

Laser bonding

Laser converting

Laser cooling

Laser engraving

Laser medicine

Laser scalpel

3D scanner

Laser turntable

Laser beam

welding

List of laser articles

List of light sources

Mercury laser

Nanolaser

Reference beam

Rytov number

Sound Amplification by Stimulated Emission of

RadiationSASER

Selective laser sintering

Spaser

Speckle pattern

Tophat beam

References

Notes

1. ^ a b Gould, R. Gordon (1959). "The LASER, Light Amplification by Stimulated Emission of Radiation". In Franken, P.A. and

Sands, R.H. (Eds.). The Ann Arbor Conference on Optical Pumping, the University of Michigan, 15 June through 18 June 1959.

p. 128. OCLC 02460155.

2. ̂  "laser". Reference.com. Retrieved 2008-05-15.

3. ̂  Conceptual physics, Paul Hewitt, 2002

4. ̂  "Schawlow and Townes invent the laser". Lucent Technologies. 1998. Retrieved 2006-10-24.

5. ^ a b Chu, Steven; Townes, Charles (2003). "Arthur Schawlow". In Edward P. Lazear (ed.),. Biographical Memoirs. vol. 83.

National Academy of Sciences. p. 202.ISBN 0-309-08699-X.

6. ̂  ""lase"". Dictionary.reference.com. Retrieved 2011-12-10.

7. ̂  Siegman, Anthony E. (1986). Lasers. University Science Books. p. 2. ISBN 0-935702-11-3.

8. ̂  Siegman, Anthony E. (1986). Lasers. University Science Books. p. 4. ISBN 0-935702-11-3.

9. ̂  "Nitrogen Laser". Light and Its Uses. Scientific American. June 1974. pp. 40–43. ISBN 0-7167-1185-0.

10. ̂  G.P. Karman, G.S. McDonald, G.H.C. New, J.P. Woerdman, "Laser Optics: Fractal modes in unstable resonators", Nature,

Vol. 402, 138, 11 November 1999.

11. ^ a b Steen, W. M. "Laser Materials Processing", 2nd Ed. 1998.

12. ̂  (Italian) "Il rischio da laser: cosa è e come affrontarlo; analisi di un problema non così lontano da noi ("The risk from laser:

what it is and what it is like facing it; analysis of a problem which is thus mot far away from us."), Programma Corso di

Formazione Obbligatorio anno 2004, Dimitri Batani (Powerpoint presentation >7Mb)". wwwold.unimib.it. Retrieved January 1,

2007.

13. ̂  The Nobel Prize in Physics 1966 Presentation Speech by Professor Ivar Waller. Retrieved 1 January 2007.

14. ̂  Joan Lisa Bromberg, The Laser in America, 1950–1970(1991), pp. 74–77 online

15. ̂  Maiman, T.H. (1960). "Stimulated optical radiation in ruby".Nature 187 (4736): 493–

494. Bibcode 1960Natur.187..493M . DOI:10.1038/187493a0.

16. ̂  Townes, Charles Hard. "The first laser". University of Chicago. Retrieved 2008-05-15.

17. ̂  Hecht, Jeff (2005). Beam: The Race to Make the Laser. Oxford University Press. ISBN 0-19-514210-1.

18. ̂  Csele, Mark (2004). "The TEA Nitrogen Gas Laser".Homebuilt Lasers Page. Archived from the original on 2007-09-11.

Retrieved 2007-09-15.

19. ̂  "Deep UV Lasers" (PDF). Photon Systems, Covina, Calif. Retrieved 2007-05-27.

20. ̂  Schuocker, D. (1998). Handbook of the Eurolaser Academy. Springer. ISBN 0-412-81910-4.

21. ̂  C. Stewen, M. Larionov, and A. Giesen, “Yb:YAG thin disk laser with 1 kW output power,” in OSA Trends in Optics and

Photonics, Advanced Solid-State Lasers, H. Injeyan, U. Keller, and C. Marshall, ed. (Optical Society of America, Washington,

DC., 2000) pp. 35-41.

22. ̂  Wu, X.; et al. (25 October 2004). "Ultraviolet photonic crystal laser". Applied Physics Letters 85 (17):

3657.arXiv:physics/0406005. Bibcode 2004ApPhL..85.3657W . DOI:10.1063/1.1808888.

23. ̂  "Picolight ships first 4-Gbit/s 1310-nm VCSEL transceivers", Laser Focus World, December 9, 2005, accessed 27 May 2006

24. ̂  F. J. Duarte, Tunable Laser Optics (Elsevier Academic, New York, 2003).

25. ̂  Palmer, Jason (2011-06-13). "Laser is produced by a living cell". BBC News. Retrieved 2011-06-13.

26. ̂  Malte C. Gather & Seok Hyun Yun (2011-06-12). "Single-cell biological lasers". Nature Photonics. Retrieved 2011-06-13.

27. ^ a b Fildes, Jonathan (2007-09-12). "Mirror particles form new matter". BBC News. Retrieved 2008-05-22.

28. ̂  Hecht, Jeff (May 2008). "The history of the x-ray laser".Optics and Photonics News (Optical Society of America) 19(5): 26–

33.

29. ̂  Robinson, Clarence A. (1981). "Advance made on high-energy laser". Aviation Week & Space Technology (23 February

1981): 25–27.

30. ̂  Charles H. Townes (2003). "The first laser". In Laura Garwin and Tim Lincoln. A Century of Nature: Twenty-One Discoveries

that Changed Science and the World. University of Chicago Press. pp. 107–12. ISBN 0-226-28413-1. Retrieved 2008-02-02.

31. ̂  Dalrymple BE, Duff JM, Menzel ER. Inherent fingerprint luminescence – detection by laser. Journal of Forensic Sciences,

22(1), 1977, 106-115

32. ̂  Dalrymple BE. Visible and infrared luminescence in documents : excitation by laser. Journal of Forensic Sciences, 28(3),

1983, 692-696

33. ̂  Kincade, Kathy and Stephen Anderson (2005) "Laser Marketplace 2005: Consumer applications boost laser sales

10%", Laser Focus World, vol. 41, no. 1. (online)

34. ̂  Steele, Robert V. (2005) "Diode-laser market grows at a slower rate", Laser Focus World, vol. 41, no. 2. (online)

35. ̂  "Green Laser 400 mW burn a box CD in 4 second". youtube.com. Retrieved 2011-12-10.

36. ̂  "Laser Diode Power Output Based on DVD-R/RW specs". elabz.com. Retrieved 2011-12-10.

37. ̂  George M. Peavy, "How to select a surgical veterinary laser", veterinary-laser.com. URL accessed 14 March 2008.

38. ̂  "Cascades™ Horizontal Stacked Arrayes". nlight.net. Retrieved March 17, 2011.

39. ̂  Heller, Arnie, "Orchestrating the world's most powerful laser." Science and Technology Review. Lawrence Livermore National

Laboratory, July/August 2005. URL accessed 27 May 2006.

40. ̂  Schewe, Phillip F.; Stein, Ben (9 November 1998)."Physics News Update 401". American Institute of Physics. Retrieved

2008-03-15.

41. ̂  PowerLabs CO2 LASER! Sam Barros 21 June 2006. Retrieved 1 January 2007.

42. ̂  "Howto: Make a DVD Burner into a High-Powered Laser". Felesmagus.com. Retrieved 2011-12-10.

43. ̂  "Police fight back on laser threat". BBC News. 8 April 2009. Retrieved 4 April 2010.

44. ̂  Peter, Pae (March 19, 2009.). "Northrop Advance Brings Era Of The Laser Gun Closer". Los Angeles Times. p. B2.

Further reading

Books

Bertolotti, Mario (1999, trans. 2004). The History of the Laser, Institute of Physics. ISBN 0-

7503-0911-3

Csele, Mark (2004). Fundamentals of Light Sources and Lasers, Wiley. ISBN 0-471-47660-9

Koechner, Walter (1992). Solid-State Laser Engineering, 3rd ed., Springer-Verlag. ISBN 0-

387-53756-2

Siegman, Anthony E. (1986). Lasers, University Science Books. ISBN 0-935702-11-3

Silfvast, William T.  (1996). Laser Fundamentals, Cambridge University Press. ISBN 0-521-

55617-1

Svelto, Orazio (1998). Principles of Lasers, 4th ed. (trans. David Hanna), Springer. ISBN 0-

306-45748-2

Taylor, Nick (2000). LASER: The inventor, the Nobel laureate, and the thirty-year patent war.

New York: Simon & Schuster. ISBN 0-684-83515-0.

Wilson, J. & Hawkes, J.F.B. (1987). Lasers: Principles and Applications, Prentice Hall

International Series in Optoelectronics, Prentice Hall. ISBN 0-13-523697-5

Yariv, Amnon (1989). Quantum Electronics, 3rd ed., Wiley. ISBN 0-471-60997-8

Bromberg, Joan Lisa (1991). The Laser in America, 1950-1970, MIT Press. ISBN 978-0-262-

02318-4

Periodicals

Applied Physics B: Lasers and Optics  (ISSN 0946-2171)

IEEE Journal of Lightwave Technology  (ISSN 0733-8724)

IEEE Journal of Quantum Electronics  (ISSN 0018-9197)

IEEE Journal of Selected Topics in Quantum Electronics  (ISSN 1077-260X)

IEEE Photonics Technology Letters  (ISSN 1041-1135)

Journal of the Optical Society of America B: Optical Physics  (ISSN 0740-3224)

Laser Focus World  (ISSN 0740-2511)

Optics Letters  (ISSN 0146-9592)

Photonics Spectra  (ISSN 0731-1230)

External links

Wikimedia Commons has

media related to: Lasers

Encyclopedia of laser physics and technology  by Dr. Rüdiger Paschotta

A Practical Guide to Lasers for Experimenters and Hobbyists  by Samuel M. Goldwasser

Homebuilt Lasers Page  by Professor Mark Csele

Powerful laser is 'brightest light in the universe'  - The world's most powerful laser as of

2008 might create supernova-like shock waves and possibly even antimatter (New

Scientist, 9 April 2008)

Homemade laser project  by Kip Kedersha

"The Laser: basic principles" an online course by Prof. F. Balembois and Dr. S.

Forget. Instrumentation for Optics, 2008

Northrop Grumman's Press Release on the Firestrike 15kw tactical laser product.

Website on Lasers 50th anniversary by APS, OSA, SPIE

Advancing the Laser anniversary site by SPIE: Video interviews, open-access articles,

posters, DVDs

Bright Idea: The First Lasers

Free software for Simulation of random laser dynamics

Video Demonstrations in Lasers and Optics  Produced by the Massachusetts Institute of

Technology (MIT). Real-time effects are demonstrated in a way that would be difficult to

see in a classroom setting.

Virtual Museum of Laser History, from the touring exhibit by SPIE

How Laser Shows Work - Laser and Exciter

    The laser generates the thin beam of intense light that is controlled and manipulated in the projector to produce the effects seen by the show spectators.

A high power, air-cooled copper vapour laser - Photo courtesy of Spectronika

What makes the light from lasers special?

    The light from lasers differs from ordinary light in several important aspects. Ordinary light from a light bulb travels randomly in all directions (unless the bulb is equipped with an integral reflector that directs the light). The light is thus incoherent. Even when incoherent light is directed with a reflector, it still spreads rapidly.

    The light from a laser is temporary and spatially coherent. This means that all of the wave-fronts of light are lined up in time and space (see diagrams). The waves of light go up and down in sync, and travel in the same direction.

    Coherent light spreads less than other types of light. For example the beam of a tightly focused flashlight would spread between 2 degrees and 5 degrees over a 3 meter (10 ft) throw distance. The sides of a laser beam are almost parallel but the light still spreads slightly. This spread is called divergence and is measured in milliradians (mrad). If a laser has a specified divergence of 5 mrad, then in the above example with a 3 meter throw (10 ft), a laser beam will spread only about 3/20 of a degree.

 

How do lasers make light?

    This is a simplified explanation of the process of stimulated emission. If you are interested in more detailed information about this subject, you should consult a science or physics book.

    Let us take the HeNe laser as an example. If a glass tube were filled with a mixture of helium and neon gas; and an electrical current were applied to the electrodes, the gas would emit light energy. This glowing gas is referred to as a plasma.  You are already familiar with this glowing gas in the form of the neon signs you see at your favorite restaurants. We now have a neon tube but not a laser so let's take a closer look at how the laser's light is produced.    Under normal conditions the electrons in a gas atom orbit at a fixed distance and pattern around the nucleus; this is the ground state or most stable configuration of the atom. When an electrical charge travels through the gas in the tube (energy is pumped into the gas), it excites or stimulates the atoms. Some of the electrons absorb this energy by jumping up to the next highest orbit.    This configuration is unstable. The electron wants to return to its regular orbit, the ground state. As the excited (stimulated) atoms in the gas relax back to the ground state, some of the energy that excited the electron(s) is emitted (released) in the form of random photons of light (see diagram below).

    This is called spontaneous emission. This is how a neon sign (or other gas discharge light such as a mercury vapour lamp) produces light. The photons travel rapidly in all directions. They are visible along the length of the neon tube or radiate outward from the light source. The spontaneous emission is not enough to cause lasing action.    Lasers are very different from neon tubes in that they amplify the glowing effect via stimulated emission. Stimulated emission can only occur when there is a "population inversion" in the energy state of the lasing medium (in this case gas).    Laser tubes are designed in a long narrow configuration with a central bore. At either end of the bore there are mirrors. These mirrors must be held in precise alignment for the laser to work properly.  In most HeNe lasers the mirrors are permanently attached or sealed onto the ends of the tube -- sometimes referred to as hard seal technology.    In higher power lasers, the mirrors are usually not mounted on the ends of the tube itself, but on an external resonator that forms part of the laser frame. This allows for changing the mirror optics or adding a littrow prism if a specific output wavelength (colour) is required. The mirrors must be perfectly aligned and parallel so that the emissions from the gas in the tube will be amplified.

    Some of the photons of light randomly emitted by the relaxing gas atoms will be traveling parallel to the bore (centre) of the laser tube. These photons will strike the mirror (high reflector) at the end of the tube and will be reflected back through the excited gas (plasma). When the photons traveling parallel to the bore are reflected from the mirrors, they oscillate back and forth between the mirrors.

An air-cooled laser tube with cooling fins - the connections for the cathode/filament are visible on the right - Photo courtesy of Laser Physics Inc.

    In their travels through the plasma, some photons strike other atoms that are in the excited state. The excited atoms are stimulated into relaxing to the ground state and releasing their duplicate photons.    The groups of photons travel back and forth through the lasing medium (gas) reflecting from the mirrors at either end. They build up sufficient energy to overcome optical losses, then lasing begins. All of the above activities take place almost instantaneously (at the speed of light) when the tube is started. The mirrors form an optical "amplifier" allowing for the amplification and stimulation of the lasing medium (gas) in the cavity (plasm tube) to produce light (photons).    If the mirrors were both totally reflective, the light would remain trapped inside the tube. In fact the high reflector is coated to 99.9% reflectivity (it should be 100% but nothing in life is perfect) so as to reflect the maximum amount of light. At the other end of the tube, the output coupler is coated between 90% and 97% reflectivity (semi-transparent mirror). Thus between 3% and 10% of the light in the tube is allowed to "leak" out as the laser beam which you see in light shows.    This "leaking" light would drain all of the energy from the plasma if it were not for the electrical power that is continuously applied to the tube. The electrical power keeps the plasma energised (ionised) and allows the laser to produce light continuously. Some types of lasers do have a cycle where energy is pumped into the lasing medium in pulses, then released in a short burst of laser energy. This type of laser is referred to as a pulsed laser and usually produces very high power levels.

 

Lasers in light shows

    There are three main types of lasers used in laser light show applications:

Ion (gas) lasers such as Argon (Ar), Krypton (Kr) or "Mixed Gas" lasers (Ar/Kr) Diode Pumped Solid State Lasers (DPSS) Diode lasers

     The laser most often used in professional light shows and displays is the Argon (Ar) laser. The argon laser gives a cyan coloured beam that can be split into blue and green beams using a yellow dichro or a prism.  A Krypton (Kr) laser can be configured to produce a number of

different colours or red only.  In some laser shows, an Argon and a Krypton laser are used as a "tandem pair" where the beams are combined to produce a "white" beam.   Full colour laser shows usually use "white light" lasers that contain a mixture of argon (Ar) and Krypton (Kr) gases in the laser tube and produces red, (sometimes yellow) green and blue from the same plasma tube.  This is simpler and more convenient that using a tandem pair of Ar and Kr lasers.

Interior of an air-cooled argon laser

    On the right is a photograph of a modern air-cooled argon laser with an integrated power supply with the top removed so you can see the internal components.    The laser tube is inside the reddish air-shroud which is used to channel the cooling air across the heatsink fins on the tube before it is blown out of the laser by the fan on the back.    On the right towards the back is the torrodial power transformer. On the left is a bank of capacitors that forms part of the power supply (most of which is not visible as it is located on a board under the laser tube).    At the back left, you can see the power cord, fuse and switch. On the back right the key interlock (for safety) and the remote control connector are visible.    This laser outputs 100Mw (1/10 of a watt) from a compact package that weighs about 7 Kg (15Lbs) and operates from 110 VAC.

Photo courtesy of Laser Physics Inc.

    The most common type of gas laser you will see is the Helium Neon (He-HeNe) laser which produces a low power red beam and is used in hobby and consumer laser shows and even in some supermarket check-out scanners.  The HeNe is rapidly being replaced by red diode lasers (the type used in laser pointers) due to their compact size, low power requirements, long life and the low cost of laser diodes.    Other common types of lasers used are Krypton (Kr) and mixed gas lasers that are usually referred to as "white light" lasers as they produce a pinkish white beam that contains a number of colours. High power solid state YAG lasers producing intense 532 nm green beams are also used, especially for outdoor shows. Copper Vapour lasers produce emerald green and gold beams.

    The laser is usually mounted on a rail or base plate so that it will be in a fixed and rigid relationship with the projector. If there is any vibration between the laser and projector, it will

affect the alignment within the projector and the alignment between the projector and distant effects such as bounce mirrors.

 

Exciter

    The exciter is the power supply for the laser that takes the multi-phase high voltage AC line power and converts it into the DC voltages and control signals that are needed to drive the plasma tube inside the laser head. 

Click Here to see the full size image (opens in a new tab) - Photo courtesy of Lexel Laser

    Lasers can be air-cooled or water cooled - the photo above shows an exciter for a water cooled ion laser. The exciter usually contains electronic control circuits to adjust the current to the laser tube, light feedback regulation and circuits to control the start-up and shut down sequencing of the laser system.  The exciter pictured above has a large, water cooled, copper "cold plate" (heatsink on the left) where the main power transistors are mounted (the passbank).  Water passes through tubes in the cold plate to keep the power transistors cool.  Water cooled exciters also typically contain flow detection devices and temperature interlocks to prevent the operation of the laser if there is insufficient water flow, or if the temperature of the system is too high.

 

Solid State Lasers

    Recently, Solid State Lasers, also called Diode Pumped Solid State (DPSS) lasers, have become available.  Rather than using a gas filled glass tube, these lasers use a laser diode to pump a crystal or a series of crystals.  The general principals of producing light by spontaneous emission discussed above are used, but rather then exciting atoms of gas, atoms in the crystal are excited to produce light.  The advantages of solid state lasers are that they are smaller, light weight,

more rugged and reliable, have blanking capability built in reducing the need for external components, and use less electrical energy.

 

Inside a DPSS Laser

    Below is a simplified diagram of a green (532 nM) DPSS laser - other colours can be generated by using different crystals and pump diodes.  There is a great deal more detail and complexity involved in the design and manufacture of these lasers but this diagram will suffice to explain the general principals.

A - A diode driver circuit is required to provide the current form the power supply (not shown) to the pump diode.  This power supply circuit has to be very precise as IR diodes are very sensitive and easily destroyed by power spikes or static discharges.  For simplicity, the rest of the electronics involved in the laser are not shown.

B - Powering a DPSS laser is an infra-red (IR) laser diode, the pump diode, emitting at 808 nM.  This frequency is in the near infrared so is faintly visible to the eye as a very dim, deep red light.  Just as with any laser, the light emitted by the diode is dangerous to the eye.

C - In order to keep the output of the pump diode at exactly 808 nM, it is mounted on a Thermoelectric Cooler (TEC) as the output frequency of diode lasers is temperature dependent.The TEC is an electronic device which transports heat from one side to another when an electric current is passed through it.  It can be use to either cool or heat a device.  In a DPSS laser, the pump diode is attached to the "cold" side while the "hot" side is attached to a heat sink to dissipate the heat that is carried away from the diode through the TEC.  It can be simply controlled by sensing the temperature of the pump diode and then using an electronic circuit to regulate the TEC so as to keep the pump diode at the correct temperature such that the diode frequency is exactly 808 nM.

D - The beam output by the pump diode is not the circular beam that we are used to seeing from an ion laser thus complex beam shaping optics must be used. The pump diode has a "fast" axis in which the beam diverges widely, and a "slow" axis in which the beam diverges far less.  The beam shaping optics are used to make the beam from the pump diode as round as possible.  It is usually not possible to make a perfectly round beam so most DPSS

lasers have a slightly elliptical beam where the beam can be as much as 2X bigger in one axis in some of the cheaper lasers.

E - A second harmonic of the 808 nM pump diode light is generated by an ND:YVO4 crystal.  This converts the light from 808 nM to 1064 nM with is also IR light but is not visible to the eye.

F - For optimal performance, the ND:YVO4 crystal must be "temperature tuned" so it is also mounted on a TEC cooler with a controller.

G - The 1064 nM light is sent to a KTP crystal which frequency doubles the Infra Red to 532 nM green light.

H - The KTP crystal must be "temperature tuned" so it is also mounted on a TEC cooler.

I - Just as in a traditional ion laser, an output coupler is used to form the laser resonator.

J - The 532 nM (green) beam emitted from the KTP is very tiny and divergent.  Beam shaping optics are used to expand and coliminate the beam to form the final laser beam output.

K - The final optic is usually an IR blocking filter.  This passes the 532 nm green laser beam and blocks any of the IR light from inside the laser that would otherwise be emitted.  This is a safety feature to prevent the emission of invisible IR light.

 

    For the technically inclined, we offer RGB Lasers for laser projection displays  A detailed paper (.pdf format) which discuss the design and development of the first, high power, all solid state RGB laser system for image projection systems by JENOPTIK Laser, Optik, Systeme GmbH.

Diode Lasers

    Diode lasers are generally only used in very low power laser equipment since they are not available in high power outputs and generally have poor beam quality.  Diode lasers are similar in structure and operation to an LED as they are a solid state device that emits light when suitable power is applied.  The internal construction of a laser diode is different from an LED and they may contain internal or external optics to focus and/or collimate the beam.  The most common use of laser diodes is ion laser pointers.

Laser (singkatan dari bahasa Inggris: Light Amplification by Stimulated Emission of Radiation) merupakan mekanisme suatu alat yang memancarkan radiasi elektromagnetik, biasanya dalam bentuk cahaya yang tidak dapat dilihat maupun dapat lihat dengan mata normal, melalui proses pancaran terstimulasi. Pancaran laser biasanya tunggal, memancarkan foton dalam pancaran koheren. Laser juga dapat dikatakan efek dari mekanika kuantum.

Dalam teknologi laser, cahaya yang koheren menunjukkan suatu sumber cahaya yang memancarkan panjang gelombang yang diidentifikasi dari frekuensi yang sama, beda fase yang konstan dan polarisasinya. Selanjutnya untuk menghasilkan sebuah cahaya yang koheren dari medium lasing adalah dengan mengontrol kemurnian, ukuran, dan bentuknya. Keluaran yang berkelanjutan dari laser dengan amplituda-konstan (dikenal sebagai CW atau gelombang berkelanjutan), atau detak, adalah dengan menggunakan teknik Q-switching, modelocking, atau gain-switching.

Dalam operasi detak, dimana sejumlah daya puncak yang lebih tinggi dapat dicapai. Sebuah medium laser juga dapat berfungsi sebagai penguat optik ketika di-seed dengan cahaya dari sumber lainnya. Sinyal yang diperkuat dapat menjadi sangat mirip dengan sinyal input dalam istilah panjang gelombang, fase, dan polarisasi; Ini tentunya penting dalam telekomunikasi serat optik.

Sumber cahaya umum, seperti bola lampu incandescent, memancarkan foton hampir ke seluruh arah, biasanya melewati spektrum elektromagnetik dari panjang gelombang yang luas. Sifat koheren sulit ditemui pada sumber cahaya atau incoherens; dimana terjadi beda fase yang tidak tetap antara foton yang dipancarkan oleh sumber cahaya. Secara kontras, laser biasanya memancarkan foton dalam cahaya yang sempit, terpolarisasi, sinar koheren mendekati monokromatik, terdiri dari panjang gelombang tunggal atau satu warna.

Beberapa jenis laser, seperti laser dye dan laser vibronik benda-padat (vibronic solid-state lasers) dapat memproduksi cahaya lewat jangka lebar gelombang; properti ini membuat mereka cocok untuk penciptaan detak singkat sangat pendek dari cahaya, dalam jangka femtodetik (10-15 detik). Banyak teori mekanika kuantum dan termodinamika dapat digunakan kepada aksi laser, meskipun nyatanya banyak jenis laser ditemukan dengan cara trial and error.Sejak diperkenalkannya laser pada tahun 1960, sebagai sebuah penyelesaian suatu masalah, maka dalam perkembangan berikutnya laser telah digunakan secara meluas, dalam bermacam-macam aplikasi modern, termasuk dalam bidang optik, elektronik, optoelektronik, teknologi informasi, sains, kedokteran, industri, dan militer. Secara umum, laser dianggap suatu pencapaian teknologi yang paling berpengaruh dalam abad ke-20.

Umumnya laser beroperasi dalam spektrum tampak pada frekuensi sekitar 1014 Hertz-15 Hertz atau ratusan ribu kali frekuensi gelombang mikro. Pada awalnya peralatan penghasil sinar laser masih serba besar dan merepotkan. Selain tidak efisien, ia baru dapat berfungsi pada suhu sangat rendah. Sinar laser yang dihasilkan belum terpancar lurus. Pada kondisi cahaya sangat cerah pun, pancarannya gampang meliuk-liuk mengikuti kepadatan atmosfer. Waktu itu, sebuah pancaran laser dalam jarak 1 km, bisa tiba di tujuan akhir pada banyak titik dengan simpangan jarak hingga hitungan meter.

Beberapa kelebihan laser diantaranya adalah kekuatan daya keluarannya yang amat tinggi sangat diminati untuk beberapa applikasinya. Namun demikian laser dengan daya yang rendah sekalipun (beberapa miliwatt) yang digunakan dalam pemancaran, masih dapat membahayakan penglihatan manusia, karena pancaran cahaya laser dapat mengakibatkan mata seseorang yang terkena mengalami kebutaan dalam sesaat atau tetap.

D I P O S K A N O L E H G U N T U R H E R M A N T O

Beberapa jenis laser, seperti laser dye dan laser vibronik benda-padat (vibronic solid-state lasers) dapat memproduksi cahaya lewat jangka lebar gelombang; properti ini membuat mereka cocok untuk penciptaan detak singkat sangat pendek dari cahaya, dalam jangka femtodetik (10-15 detik). Banyak teori mekanika kuantum dan termodinamika dapat digunakan kepada aksi laser, meskipun nyatanya banyak jenis laser ditemukan dengan cara trial and error.Sejak diperkenalkannya laser pada tahun 1960, sebagai sebuah penyelesaian suatu masalah, maka dalam perkembangan berikutnya laser telah digunakan secara meluas, dalam bermacam-macam aplikasi modern, termasuk dalam bidang optik, elektronik, optoelektronik, teknologi informasi, sains, kedokteran, industri, dan militer. Secara umum, laser dianggap suatu pencapaian teknologi yang paling berpengaruh dalam abad ke-20.

Umumnya laser beroperasi dalam spektrum tampak pada frekuensi sekitar 1014 Hertz-15 Hertz atau ratusan ribu kali frekuensi gelombang mikro. Pada awalnya peralatan penghasil sinar laser masih serba besar dan merepotkan. Selain tidak efisien, ia baru dapat berfungsi pada suhu sangat rendah. Sinar laser yang dihasilkan belum terpancar lurus. Pada kondisi cahaya sangat cerah pun, pancarannya gampang meliuk-liuk mengikuti kepadatan atmosfer. Waktu itu, sebuah pancaran laser dalam jarak 1 km, bisa tiba di tujuan akhir pada banyak titik dengan simpangan jarak hingga hitungan meter.

Beberapa kelebihan laser diantaranya adalah kekuatan daya keluarannya yang amat tinggi sangat diminati untuk beberapa applikasinya. Namun demikian laser dengan daya yang rendah sekalipun (beberapa miliwatt) yang digunakan dalam pemancaran, masih dapat membahayakan penglihatan manusia, karena pancaran cahaya laser dapat mengakibatkan mata seseorang yang terkena mengalami kebutaan dalam sesaat atau tetap.

D I P O S K A N O L E H G U N T U R H E R M A N T O   D I   1 1 : 2 7   0 K O M E N T A R   L I N K K E P O S T I N G I N I

L A B E L :   T E C H N O

Pemenang Nobel Fisika 2009:

Charles K Kao (warga AS

kelahiran Shanghai, China),

Williard S Boyle, dan George E

Smith (AS).

Charles K Kao dihargai atas

terobosannya menemukan

teknologi transmisi cahaya

melalui serat optik. Penemuan

Kao inilah yang menjadi

pondasi jaringan

telekomunikasi modern saat

ini dari telepon hingga

internet kecepatan tinggi!

Sementara dua ilmuwan lainnya diganjar hadiah bergengsi tersebut karena sebagai penemu CCD (charged-couple device).

Teknologi yang ditemukan Boyle dan Smith itu merupakan bagian penting kamera digital.

“Hal itu telah merevolusi dunia fotografi, karena sekarang cahaya bisa ditangkap secara elektronik,” demikian pendapat

penilaian panel juri Nobel. Dengan CCD, kamera digital dengan lensa raksasa seperti yang dibawa teleskop ruang angkasa

Hubble bisa memotret objek antariksa yang sangat jauh dan indah!

Apa itu Serat Optik ?

Serat optik adalah saluran transmisi yang terbuat dari kaca atau plastik yang digunakan untuk mentransmisikan sinyal cahaya

dari suatu tempat ke tempat lain. Cahaya yang ada di dalam serat optik sulit keluar karena indeks bias dari kaca lebih besar

daripada indeks bias dari udara. Sumber cahaya yang digunakan adalah laser karena laser mempunyai spektrum yang sangat

sempit. Kecepatan transmisi serat optik sangat tinggi sehingga sangat bagus digunakan sebagai saluran komunikasi.

Untuk  Apa Serat Optik Digunakan ?

Serat optik umumnya digunakan dalam sistem telekomunikasi serta dalam pencahayaan, sensor, dan optik pencitraan.

Serat optik terdiri dari 2 bagian, yaitu cladding dan core. Cladding adalah selubung dari core. Cladding mempunyai indek bias

lebih rendah dari pada core akan memantulkan kembali cahaya yang mengarah keluar dari core kembali kedalam core lagi.

Efisiensi dari serat optik ditentukan oleh kemurnian dari bahan penyusun gelas. Semakin murni bahan gelas, semakin sedikit

cahaya yang diserap oleh serat optik.

Pembagian Serat optik dapat dilihat dari 2 macam perbedaan :

1. Berdasarkan Mode yang dirambatkan :

Single mode: serat optik dengan core yang sangat kecil, diameter mendekati panjang gelombang sehingga cahaya yang masuk

ke dalamnya tidak terpantul-pantul ke dinding cladding. Multi mode: serat optik dengan diameter core yang agak besar yang membuat laser di dalamnya akan terpantul-pantul di

dinding cladding yang dapat menyebabkan berkurangnya bandwidth dari serat optik jenis ini.

2. Berdasarkan indeks bias core :

Step indeks: pada serat optik step indeks, core memiliki indeks bias yang homogen.

Graded indeks: indeks bias core semakin mendekat ke arah cladding semakin kecil. Jadi pada graded indeks, pusat core

memiliki nilai indeks bias yang paling besar. Serat graded indeks memungkinkan untuk membawa bandwidth yang lebih besar,

karena pelebaran pulsa yang terjadi dapat diminimalkan.

agian-bagian serat optik jenis single mode

Reliabilitas dari serat optik dapat ditentukan dengan satuan BER (Bit Error Rate). Salah satu ujung serat optik diberi masukan

data tertentu dan ujung yang lain mengolah data itu. Dengan intensitas laser yang rendah dan dengan panjang serat mencapai

beberapa km, maka akan menghasilkan kesalahan. Jumlah kesalahan persatuan waktu tersebut dinamakan BER. Dengan

diketahuinya BER maka, Jumlah kesalahan pada serat optik yang sama dengan panjang yang berbeda dapat diperkirakan

besarnya.

Sejarah Fiber Optic

Penggunaan cahaya sebagai pembawa informasi sebenarnya sudah banyak digunakan sejak zaman dahulu, baru sekitar tahun

1930-an para ilmuwan Jerman mengawali eksperimen untuk mentransmisikan cahaya melalui bahan yang bernama serat optik.

Percobaan ini juga masih tergolong cukup primitif karena hasil yang dicapai tidak bisa langsung dimanfaatkan, namun harus

melalui perkembangan dan penyempurnaan lebih lanjut lagi. Perkembangan selanjutnya adalah ketika para ilmuawan Inggris

pada tahun 1958 mengusulkan prototipe serat optik yang sampai sekarang dipakai yaitu yang terdiri atas gelas inti yang

dibungkus oleh gelas lainnya. Sekitar awal tahun 1960-an perubahan fantastis terjadi di Asia yaitu ketika para ilmuwan Jepang

berhasil membuat jenis serat optik yang mampu mentransmisikan gambar.

Di lain pihak para ilmuwan selain mencoba untuk memandu cahaya melewati gelas (serat optik) namun juga mencoba untuk

”menjinakkan” cahaya. Kerja keras itupun berhasil ketika sekitar 1959 laser ditemukan. Laser beroperasi pada daerah

frekuensi tampak sekitar 1014 Hertz-15 Hertz atau ratusan ribu kali frekuensi gelombang mikro.

Pada awalnya peralatan penghasil sinar laser masih serba besar dan merepotkan. Selain tidak efisien, ia baru dapat berfungsi

pada suhu sangat rendah. Laser juga belum terpancar lurus. Pada kondisi cahaya sangat cerah pun, pancarannya gampang

meliuk-liuk mengikuti kepadatan atmosfer. Waktu itu, sebuah pancaran laser dalam jarak 1 km, bisa tiba di tujuan akhir pada

banyak titik dengan simpangan jarak hingga hitungan meter.

Sekitar tahun 60-an ditemukan serat optik yang kemurniannya sangat tinggi, kurang dari 1 bagian dalam sejuta. Dalam bahasa

sehari-hari artinya serat yang sangat bening dan tidak menghantar listrik ini sedemikian murninya, sehingga konon,

seandainya air laut itu semurni serat optik, dengan pencahayaan cukup kita dapat menonton lalu-lalangnya penghuni dasar

Samudera Pasifik.

Seperti halnya laser, serat optik pun harus melalui tahap-tahap pengembangan awal. Sebagaimana medium transmisi cahaya,

ia sangat tidak efisien. Hingga tahun 1968 atau berselang dua tahun setelah serat optik pertama kali diramalkan akan menjadi

pemandu cahaya, tingkat atenuasi (kehilangan)-nya masih 20 dB/km. Melalui pengembangan dalam teknologi material, serat

optik mengalami pemurnian, dehidran dan lain-lain. Secara perlahan tapi pasti atenuasinya mencapai tingkat di bawah 1

dB/km.

Tahun 80-an, bendera lomba industri serat optik benar-benar sudah berkibar. Nama-nama besar di dunia pengembangan serat

optik bermunculan. Charles K. Kao diakui dunia sebagai salah seorang perintis utama. Dari Jepang muncul Yasuharu Suematsu.

Raksasa-raksasa elektronik macam ITT atau STL jelas punya banyak sekali peranan dalam mendalami riset-riset serat optik.

Time Line Pengembangan Fiber Optik

1917 Theory of stimulated emission Albert Einstein mengajukanm sebuah teori tentang emisi terangsang dimana jika ada atom

dalam tingkatan energi tinggi 1954 “Maser” developed Charles Townes, James Gordon, dan Herbert Zeiger di Columbia

University mengembangkankan “maser” yaitu microwave amplification by stimulated emission of radiation, dimana molekul

dari gas amonia memperkuat dan menghasilkan gelombang. . Pekerjaan ini menghabiskan waktu tiga tahun sejak ide Townes

pada tahun 1951 untuk mengambil manfaat dari osilasi frekuensi tinggi molekular untuk membangkitkan gelombang dengan

penjang gelombang pendek pada gelombang radio. 1958 Pengenalan Konsep Laser Townes dan ahli fisika Arthur Schawlow

mempublikasikan paper yang menunjukan bahwa maser dapat dibuat untuk dioperasikan pada daerah infra merah dan

optik. .Paper ini menjelaskan tentang konsep laser (light amplification by stimulated emission of radiation)

1960 ditemukannya Continuously operating helium-neon gas laser Laboratorium Riset Bell dan Ali Javan serta koleganya

William Bennett, Jr., dan Donald Herriott menemukan sebuah continuously operating helium-neon gas laser. 1960

Ditemukannya Operable laser Theodore Maiman, seorang fisikawan dan insinyur elektro di Hughes Research Laboratories,

menemukan operable laser dengan menggunakan sebuah kristal batu rubi sintesis sebagai medium. 1961 Glass fiber

demonstration Peneliti industri Elias Snitzer dan Will Hicks mendemontrasikan sinar laser yang diarahkan melalui serat gelas

yang tipis. Inti serat gelas tersebut cukup kecil yang membuat cahaya hanya dapat melewati satu bagian saja tetapi banyak

ilmuwan menyatakan bahwa serat tidak cocok untuk komunikasi karena rugi rugi cahaya yang terjadi karena melewati jarak

yang sangat jauh. 1961 Penggunaan ruby laser untuk keperluan medis Penggunaan laser yang dihasilkan dari batu Rubi yang

pertama, Charles Campbell of the Institute of Ophthalmology at Columbia- Presbyterian Medical Center dan Charles Koester of

the American Optical Corporation menggunakan prototipe ruby laser photocoagulator untuk menghancurkan tumor pada retina

pasien. 1962 Pengembangan Gallium arsenide laser Tiga group riset terkenal yaitu General Electric, IBM, dan MIT’s Lincoln

Laboratory secara simultan mengembangkan gallium arsenide laser yang mengkonversikan energi listrk secara langsung ke

dalam cahaya infra merah dan perkembangan selanjutnya digunakan untuk pengembangan CD dan DVD player serta

penggunaan laser printer. 1963 Heterostructures Ahli fisika Herbert Kroemer mengajukan ide yaitu heterostructures, kombinasi

dari lebih dari satu semikonduktor dalam layer-layer untuk mengurangi kebutuhan energi untuk laser dan membantu untuk

dapat bekerja lebih efisien. Heterostructures ini nantinya akan digunakan pada telepon seluler dan peralatan elektronik lainnya.

1966 kertas Landmark pada optical fiber Charles Kao dan George Hockham yang melakukan penelitian di Standard

Telecommunications Laboratories Inggris mempublikasikan landmark paper yang mendemontrasikan bahwa fiber optik dapat

mentransmisikan sinar laser yang sangat sedikit rugi-ruginya jika gelas yang digunakan sangat murni. Dengan penemuan ini

kemudian para peneliti lebih fokus pada bagaimana cara memurnikan bahan gelas. 1970 Fiber Optik yang memenuhi standar

kemurnian. Ilmuwan Corning Glass Works yaitu Donald Keck, Peter Schultz, dan Robert Maurer melaporkan penemuan fiber

optik yang memenuhi standar yang telah ditentukan oleh Kao dan Hockham. Gelas yang paling murni yang dibuat terdiri atas

gabungan silika dalam tahap uap dan mampu mengurangi rugi-rugi cahaya kurang dari 20 decibels per kilometer. Pada 1972

tim ini menemukan gelas dengan rugi-rugi cahaya hanya 4 decibels per kilometer. Juga pada tahun 1970, Morton Panish dan

Izuo Hayashi dari Bell Laboratories dengan tim Ioffe Physical Institute di Leningrad, mendemontrasikan semiconductor laser

yang dapat dioperasikan pada temperatur ruang. Kedua penemuan tersebut merupakan terobosan dalam komersialisasi

penggunaan fiber optik. 1973 Proses Chemical vapor deposition John MacChesney dan Paul O. Connor pada Bell Laboratories

mengembangkan proses chemical vapor deposition process yang memanaskan uap kimia dan oksigen ke bentuk

ultratransparent glass yang dapat diproduksi masal ke dalam fiber optik yang mempunyai rugi-rugi sangat kecil. 1975

Komersialisasi Pertama dari semiconductor laser Insinyur pada Laser Diode Labs mengembangkan semiconductor laser

komersial pertama yang dapat dioperasikan pada suhu kamar. 1977 Perusahaan telepon menguji coba penggunaan fiber optic

Perusahaan telepon memulai penggunaan fiber optik yang membawa lalu lintas telepon. GTE membuka jalur antara Long

Beach dan Artesia, California, yang menggunakan transmisi light-emitting diode. Bell Labs mendirikan sambungan yang sama

pada sistem telepon di Chicago dengan jarak 1,5 mil di bawah tanah yang menghubungkan 2 s switching station.

1980 Sambungan Fiber-optic telah ada di Kota kota besar di Amerika AT&T mengumumkan akan menginstal fiber-optic yang

menghubungkan kota kota antara Boston dan Washington D.C. kemudian dua tahun kemudian MCI mengumumkan untuk

melakukan hal yang sama. 1987 “Doped” fiber amplifiers David Payne di University of Southampton memperkenalkan fiber

amplifiers yang dikotori oleh elemen erbium. optical amplifiers abru ini mampu menaikan sinyal cahaya tanpa harus

mengkonversikan terlebih dahulu ke dalam energi listrik. 1988 Kabel Pertama Transatlantic Fiber-Optic Kabel Translantic yang

pertama menggunakan fiber glass yang sangat transparan sehingga repeater hanya dibutuhkanb ketika sudah mencapai

40mil. 1991 Optical Amplifiers Emmanuel Desurvire di Bell Laboratories serta David Payne dan P. J. Mears dari University of

Southampton mendemontrasikan optical amplifiers yang terintegrasi dengan kabel fiber optic tersebut. Keuntungannya adalah

dapat membawa informasi 100 kali lebih cepat dari pada kabel electronic amplifier. 1996 optic fiber cable yang menggunakan

optical amplifiers ditaruh di samudera pasifik TPC-5, sebuah optic fiber merupakan fiber optic pertama yang menggunakan

optical amplifiers. Kabel ini melewati samudera pasifik mulai dari San Luis Obispo, California, ke Guam, Hawaii, dan Miyazaki,

Japan, dan kembali ke Oregon coast dan mampu untuk menangani 320,000 panggilan telepon. 1997 Fiber Optic

menghubungkan seluruh dunia Fiber Optic Link Around the Globe (FLAG) menjadi jaringan abel terpanjang di seluruh dunia

yang menyediakan infrastruktur untuk generasi internet terbaru.

Generasi Perkembangan Serat Optik

Berdasarkan penggunaannya maka sistem komunikasi serat optik (SKSO) dibagi menjadi 4 tahap generasi yaitu :

1. Generasi pertama (mulai 1975)

Sistem masih sederhana dan menjadi dasar bagi sistem generasi berikutnya, terdiri dari : alat encoding : mengubah input

(misal suara) menjadi sinyal listrik transmitter : mengubah sinyal listrik menjadi sinyal gelombang, berupa LED dengan panjang

gelombang 0,87 mm. serat silika : sebagai penghantar sinyal gelombang repeater : sebagai penguat gelombang yang melemah

di perjalanan receiver : mengubah sinyal gelombang menjadi sinyal listrik, berupa fotodetektor alat decoding : mengubah

sinyal listrik menjadi output (misal suara) Repeater bekerja melalui beberapa tahap, mula-mula ia mengubah sinyal gelombang

yang sudah melemah menjadi sinyal listrik, kemudian diperkuat dan diubah kembali menjadi sinyal gelombang. Generasi

pertama ini pada tahun 1978 dapat mencapai kapasitas transmisi sebesar 10 Gb.km/s.

2. Generasi kedua (mulai 1981)

Untuk mengurangi efek dispersi, ukuran teras serat diperkecil agar menjadi tipe mode tunggal. Indeks bias kulit dibuat sedekat-

dekatnya dengan indeks bias teras. Dengan sendirinya transmitter juga diganti dengan diode laser, panjang gelombang yang

dipancarkannya 1,3 mm. Dengan modifikasi ini generasi kedua mampu mencapai kapasitas transmisi 100 Gb.km/s, 10 kali lipat

lebih besar daripada generasi pertama.

3. Generasi ketiga (mulai 1982)

Terjadi penyempurnaan pembuatan serat silika dan pembuatan chip diode laser berpanjang gelombang 1,55 mm. Kemurnian

bahan silika ditingkatkan sehingga transparansinya dapat dibuat untuk panjang gelombang sekitar 1,2 mm sampai 1,6 mm.

Penyempurnaan ini meningkatkan kapasitas transmisi menjadi beberapa ratus Gb.km/s.

4. Generasi keempat (mulai 1984)

Dimulainya riset dan pengembangan sistem koheren, modulasinya yang dipakai bukan modulasi intensitas melainkan modulasi

frekuensi, sehingga sinyal yang sudah lemah intensitasnya masih dapat dideteksi. Maka jarak yang dapat ditempuh, juga

kapasitas transmisinya, ikut membesar. Pada tahun 1984 kapasitasnya sudah dapat menyamai kapasitas sistem deteksi

langsung. Sayang, generasi ini terhambat perkembangannya karena teknologi piranti sumber dan deteksi modulasi frekuensi

masih jauh tertinggal. Tetapi tidak dapat disangkal bahwa sistem koheren ini punya potensi untuk maju pesat pada masa-masa

yang akan datang.

5. Generasi kelima (mulai 1989)

Pada generasi ini dikembangkan suatu penguat optik yang menggantikan fungsi repeater pada generasi-generasi sebelumnya.

Sebuah penguat optik terdiri dari sebuah diode laser InGaAsP (panjang gelombang 1,48 mm) dan sejumlah serat optik dengan

doping erbium (Er) di terasnya. Pada saat serat ini disinari diode lasernya, atom-atom erbium di dalamnya akan tereksitasi dan

membuat inversi populasi*, sehingga bila ada sinyal lemah masuk penguat dan lewat di dalam serat, atom-atom itu akan

serentak mengadakan deeksitasi yang disebut emisi terangsang (stimulated emission) Einstein. Akibatnya sinyal yang sudah

melemah akan diperkuat kembali oleh emisi ini dan diteruskan keluar penguat. Keunggulan penguat optik ini terhadap repeater

adalah tidak terjadinya gangguan terhadap perjalanan sinyal gelombang, sinyal gelombang tidak perlu diubah jadi listrik dulu

dan seterusnya seperti yang terjadi pada repeater. Dengan adanya penguat optik ini kapasitas transmisi melonjak hebat sekali.

Pada awal pengembangannya hanya dicapai 400 Gb.km/s, tetapi setahun kemudian kapasitas transmisi sudah menembus

harga 50 ribu Gb.km/s.

6. Generasi keenam

Pada tahun 1988 Linn F. Mollenauer memelopori sistem komunikasi soliton. Soliton adalah pulsa gelombang yang terdiri dari

banyak komponen panjang gelombang. Komponen-komponennya memiliki panjang gelombang yang berbeda hanya sedikit,

dan juga bervariasi dalam intensitasnya. Panjang soliton hanya 10-12 detik dan dapat dibagi menjadi beberapa komponen yang

saling berdekatan, sehingga sinyal-sinyal yang berupa soliton merupakan informasi yang terdiri dari beberapa saluran

sekaligus (wavelength division multiplexing). Eksperimen menunjukkan bahwa soliton minimal dapat membawa 5 saluran yang

masing-masing membawa informasi dengan laju 5 Gb/s. Cacah saluran dapat dibuat menjadi dua kali lipat lebih banyak jika

dibunakan multiplexing polarisasi, karena setiap saluran memiliki dua polarisasi yang berbeda. Kapasitas transmisi yang telah

diuji mencapai 35 ribu Gb.km/s.

Cara kerja sistem soliton ini adalah efek Kerr, yaitu sinar-sinar yang panjang gelombangnya sama akan merambat dengan laju

yang berbeda di dalam suatu bahan jika intensitasnya melebihi suatu harga batas. Efek ini kemudian digunakan untuk

menetralisir efek dispersi, sehingga soliton tidak akan melebar pada waktu sampai di receiver. Hal ini sangat menguntungkan

karena tingkat kesalahan yang ditimbulkannya amat kecil bahkan dapat diabaikan. Tampak bahwa penggabungan ciri

beberapa generasi teknologi serat optik akan mampu menghasilkan suatu sistem komunikasi yang mendekati ideal, yaitu yang

memiliki kapasitas transmisi yang sebesar-besarnya dengan tingkat kesalahan yang sekecil-kecilnya yang jelas, dunia

komunikasi abad 21 mendatang tidak dapat dihindari lagi akan dirajai oleh teknologi serat optik.

Sumber : http://anangss.blogspot.com/2009/10/serat-optik-atau-fiber-optic.html

Wireless pointer

Dalam persiapan presentasi tentunya dibutuhkan alat-alat pendukungnya seperti LCD projector, layar putih di dinding, dan tentunya komputer/notebook, seringkali kita jauh dari notebook dan harus bolak-balik antara tempat presentasi ke area notebook hanya ingin menekan tombol navigasi page up/pagedown ke halaman presentasi selanjutnya, dengan adanya wireless presenter ini semoga bisa membantu anda dalam berpresentasi.

berikut gambar dari wireless pointernya :

F

ungsi :

1. Memudahkan untuk presentasi , tidak perlu bolak-balik ke komputer/notebook jika hanya menekan tombol page up/ page down,

2. Cahaya laser : cahaya lingkaran merah yang nampak di halaman layar putih di dinding untuk menunjukan point presentasi.

Cara penggunaan :

1. Tancapkan usb transmitter ke komputer/notebook,

2. Kemudian tunggu hingga indicator LED menyala kedap-kedip,

3. Wireless pointer siap digunakan, tekan page up / page down.

Cara kerja antara Pen laser dan usb transmitter :

Berawal dari input berupa navigasi page down / page up dari Pen,

Kemudian diarakan ke bagian sinyal pengirim dari pen,

Lalu diterima di sinyal penerima usb transmitter,

Dan diteruskan ke tombol page down / up, seperti tombol keyboard di komputer/notebook

Terjadinya pengiriman dan penerimaan sinyal remote control menggunakan LED(Light Emitting Diode) yang berfungsi sebagai pengirim(transmitter) pola sinar infra merah. LED infra merah adalah sejenis lampu kecil yang memiliki dioda yang akan memancarkan cahaya infra merah apabila diberi arus. Teknologi ini seperti digunakan dalam metode bluetooth

Keterangan :

A. Deret Pulsa/kode/morse,

B. Sinyal 27.9 MHz,

C. Sinyal Transmisi,

D. Pola sinkronisasi 4, masing-masing 2.1 mili detik, dengan spasi 700 mikro detik,

E. Pola pulsa, masing-masing 700 mikro detik, dengan spasi 700 mikro detik juga,

F. Pola Sinkronisasi ulang.

Sinyal infra merah yang dikirimkan tidak akan dapat dilihat oleh mata kita, karena sinar infra merah tidak termasuk gelombang elektromagnetik pada spectrum cahaya tampak. Namun sinar tersebut dapat terbaca oleh receiver yang ada pada peralatan elektronik yang menerima sinyal tersebut.

Cara kerja sinar laser / LED dioda :

Bermula dari sebuah dioda berukuran 808nm yang memancarkan sinar lurus,

Melalui lensa pengfokusan, disinilah ruang untuk mengumpulkan seberkas sinar, diteruskan ke

Lensa perluasan(lensa cekung) cahaya bisa dipantulkan sampai jauh),

Melewati lensa kollimator pelurusan sinar yang stabil ), dan dikeluarkan ke ruangan terbuka,

Dan akhirnya terbias ke permukaan datar/dinding berupa lingkaran merah seukuran jagung

selain Led warna merah, juga ada warna violet,hijau,biru.

 Sejarah dan Manfaat Sinar Laser Bagi Kehidupan

LASER (singkatan dari bahasa Inggris: Light Amplification by Stimulated Emission of Radiation) , Laser memperkuat cahaya. Laser dapat mengambil berkas cahaya yang lemah dan membuatnya menjadi berkas yang kuat. Beberapa laser menghasilkan berkas yang sangat kuat sehingga dapat membakar lubang kecil di dalam selembar besi dalam waktu kurang dari satu detik.

Sinar laser dapat mencapai jarak jauh melalui angkasa luar tanpa menyebar dan menjadi lemah. Karena itulah, sinar laser menjadi alat komunikasi penting dalam berkomunikasi dalam jaman angkasa luar. Banyak kegunaan laser sudah ditemukan dalam ilmu kedokteran, ilmu pengetahuan, dan industri.

Ilmuwan menganggap cahaya sebagai gelombang yang bergerak. Jarak dari kulit sebuah gelombang ke kulit berikutnya disebut panjang gelombang. Cahaya dari matahari atau dari lampu adalah campuran banyak panjang gelombang. Setiap panjang gelombang yang berbeda menghasilkan warna yang berbeda.

Sinar laser terbuat dari cahaya yang semuanya terdiri dari panjang gelombang yang sama. Berkas cahaya dalam cahaya biasa mengalir ke arah yang berbeda. Sinar laser bergerak dalam arah yang sama persis. Sinar laser tidak menyebar dan tidak melemah.

Pada awal perkembangannya, orang tidak menyebut dengan nama laser. Para ahli masa itu menyebutnya sebagai MASER (Microwave Amplification by the Stimulated Emission of Radiation. Dan orang yang disebut-sebut pertama kali mengungkapkan keberadaan maser adalah Albert Einstein antara tahun 1916 - 1917. Ilmuwan yang terkenal eksentrik ini juga yang pertama kali berpendapat bahwa cahaya atau sinar bukan hanya

terdiri dari gelombang elektromagnetik, tapi juga bermuatan partikel dan energi. Dan dikenal lah apa yang disebut sebagai radiasi. Tapi maser dari Einsten ini baru sebatas teori. Teknologi pada dekade kedua abad 20 belum mampu mewujudkannya. Disamping itu, banyak ilmuwan yang menganggap teori dari Eisntein itu sebagai teori yang kontroversial.

Pada tahun-tahun berikutnya, terlebih pada perang dunia kedua, maser lebih banyak digunakan untuk kepentingan militer, yaitu untuk pengembangan radar. Hingga akhirnya Charles H. Townes, James Gordon, dan Herbert Zeiger, berhasil membuat maser dengan menggunakan gas Amoniak. Dan inilah maser yang pertama kali dibuat orang. Keberhasilan itu dipublikasikan pada tahun 1954. Itu merupakan maser dengan satu tingkat energi. Selanjutnya ide emisi dua tingkat untuk mempertahankan inversi pada maser telah dikembangkan oleh dua orang ilmuwan Sovyet, Nikolai Basov dan Alexander Prokhorov. Karena sumbangannya yang sangat penting ini dalam pengembangan maser, Charles H. Townes, Nikolai Basov, dan Alexander Prokhorov berbagi hadiah Nobel bidang Fisika pada tahun 1964.

Charles H. Townes memang orang yang berperan penting dalam dunia maser. Sebelumnya beliau bersama Arthur Schawlow telah meneliti kemungkinan pembuatan maser optik (yang kemudian berkembang menjadi laser) dan sinar infra merah. Rincian penelitian itu diterbitkan pada bulan Desember 1958. Namun mereka berdua masih menemui kesulitan dan pembuatan laser (maser optik). Hingga akhirnya sebelum memasuki tahun 1960 Theodore Maiman bisa mewujudkan kerja sinar laser. Maiman menggunakan silinder batu Ruby untuk memicu timbulnya laser hingga laser buatannya dikenal sebagai Ruby Laser. Tapi Ruby Laser hanya mampu bekerja pada energi tingkat ketiga. Setelah memasuki tahun 1960, Peter Sorokin dan Mirek Stevenson mulai mengembangkan laser tingkat keempat yang pertama. Tapi itu pun masih sebatas teori dan tujuan untuk merealisasikannya masih belum tercapai. Namun demikian sejak saat itu lah era laser dimulai.

Sekilas bahwa Theodore Maiman dianggap sebagai orang yang pertama kali berhasil membuat laser (bukan maser). Tapi sebenarnya ada orang lain yang telah mendahuluinya yaitu Gordon Gould. Pada tahun 1958, Gordon Gould kabarnya telah berhasil membuat maser optik (laser) bahkan dia juga yang dianggap sebagai orang yang pertama kali menggunakan istilah Laser (Light Amplification by the Stimulated Emission of Radiation). Tapi Gordon gagal mendaftarkan paten laser-nya pada tahun 1959. Hingga pada tahun 1977 Gordon memenangkan paten tersebut. Butuh waktu 8 tahun untuk mendapatkan pengakuan itu.

Pada masa yang hampir bersamaan juga beberapa ilmuwan lain berhasil membuat laser dengan menggunakan bahan yang berbeda. Misalnya Ali Javan, William Bennet dan Donald Herriot yang membuat laser dengan media gas helium dan neon pada tahun 1960 dan keberhasilannya baru dipublikasikan pada tahun 1961. Kumar N. Patel membuat laser dengan perantaraan karbondioksida, nitrogen, dan helium pada tahun 1964. Dan pada tahun yang sama juga (1964), Earl Bell membuat laser dengan bantuan helium dan merkuri. Para ilmuwan ini dianggap pembuat untuk laser gas karena bahan-bahan yang mereka gunakan untuk membuat laser pada umumnya berupa zat gas.

Perkembangan yang cukup penting terjadi pada tahun 1962 ketika seorang ilmuwan yang bekerja pada perusahaan General Electric, Robert Hall, menemukan laser semikonduktor berukuran mini dengan biaya murah. Biasanya mesin atau peralatan pemroduksi sinar laser berukuran besar. Laser buatan Rober Hall inilah yang hingga kini digunakan pada perangkat vcd dan dvd player, printer laser, pembaca kode bar, drive pada CPU, sistem komunikasi yang menggunakan serat optik, dan sebagainya.

Sebuah penemuan yang revolusioner dibuat pada tahun 1970 ketika Charles Kao dan George Hockham berhasil membuat apa yang sekarang disebut serat optik (fiberglass). Mereka berdua memang tidak membuat laser, tapi penemuannya sangat penting dalam penggunaan aplikasi laser. Dan seperti kita tahu, serat optik banyak digunakan dalam bidang komunikasi. Bidang inilah yang memang dianggap sebagai pengguna terbesar aplikasi laser. Laser dan serat optik memang dua penemuan yang sangat saling mendukung.

Ada berbagai jenis laser. Medium laser bisa padat, gas, cair atau semikonduktor. Laser biasanya ditentukan oleh jenis bahan yang digunakan oleh penguatnya

Solid-state laser material telah dikuatkan terdistribusi dalam matriks padat (seperti ruby atau neodymium: yttrium-aluminium garnet laser yag). Laser neodymium-yag memancarkan cahaya inframerah pada 1.064 nanometer (nm).

laser Gas (helium dan helium-neon, hene, merupakan laser gas yang paling umum) memiliki output utama dari lampu inframerah. CO2 laser memancarkan energi jauh dr inframerah, dan digunakan untuk memotong material keras.

laser Excimer (nama ini berasal dari istilah excited dan dimers) menggunakan gas reaktif, seperti klorin dan fluorin, dicampur dengan gas inert seperti argon, kripton atau xenon. Ketika elektrik dirangsang, molekul pseudo (dimer). Ketika lased, dimer menghasilkan cahaya dalam kisaran ultraviolet.

Dye laser menggunakan pewarna organik kompleks, seperti rhodamine 6g, dalam larutan cair atau suspensi sebagai media penguat.

Semiconductor laser, kadang-kadang disebut dioda laser, laser yg tidak solid-state. Perangkat elektronik yg menggunakan ini umumnya sangat kecil dan menggunakan daya yang rendah. Mereka dapat dibangun menjadi array yang lebih besar, seperti sumber penulisan dalam beberapa printer laser atau CD player.

Dalam kehidupan sehari-hari, laser digunakan pada berbagai bidang. Dalam penggunaannya, energi laser yang terpancar tiap satuan waktu dinyatakan dengan orde dari beberapa mW(Laser yand digunakan dalam system audio laser disk) sampai dengan beberapa MW(Laser yang digunakan untuk senjata). Besarnya energi laser yang dipilih bergantung pada penggunaannya. Pemanfaatan sinar laser misalnya pada bidang kedokteran, pelayanan (jasa), industri, astronomi, fotografi, elektronika, dan komunikasi.

Dalam bidang kedokteran dan kesehatan, sinar laser digunakan antara lain untuk mendiagnosis penyakit, pengobatan penyakit, dan perbaikan suatu cacat serta penbedahan. Pada bidang industri, sinar laser bermanfaat untuk pengelasan, pemotongan lempeng baja, serta untuk pengeboran. Pada bidang astronomi, sinar laser berdaya tinggi dapat digunakan untuk mengukur jarak Bumi Bulan dengan teliti. Dala bidang fotografi, laser mampu menghasilkan bayangan tiga dimensi dari suatu benda, disebut holografi. Dalam bidang elektronika, laser solid state berukuran kecil digunakan dalam system penyimpanan memori optik dalam

computer. Dalam bidang komunikasi, laser berfungsi untuk memperkuat cahaya sehingga dapat menyalurkan suara dan sinyal gambar melalui serat optik

Demikian presentasi yang bisa kami berikan, semoga kita selalu mengikuti perkembangan teknologi yang berjalan dan bisa mengembangkan sesuatu teknologi baru, semakin berkembangnya teknologi semakin membantu aktivitas kehidupan dengan mudah dan efektif,

namun masih banyak teknologi yang disalahgunakan, dan maraknya cibercrime ( kejahatan di dunia internet ), tetapi bila teknologi itu digunakan dengan tatacara yang benar maka seperti segarnya embun dipagi hari dan pelangi yang bersinar.

Laser adalah suatu divais yang memancarkan gelombang elektromagnetik melewati

suatu proses yang dinamakan emisi spontan. Istilah laser merupakan singkatan dari light

amplification by stimulated emission of radiation. Berkas laser umumnya sangat koheren,

yang mengandung arti bahwa cahaya yang dipancarkan tidak menyebar dan rentang

frekuensinya sempit (monochromatic light). Laser merupakan bagian khusus dari sumber

cahaya. Sebagian besar sumber cahaya, emisinya tidak koheren, spektrum frekuensinya lebar,

dan phasenya bervariasi terhadap waktu dan posisi. Daerah kerja divais laser tidak terbatas

pada spektrum cahaya tampak saja tetapi dapat bekerja pada daerah frekuensi yang luas, Oleh

karena itu, divais tersebut dapat berupa laser infa red, laser ultra violet, laser X-ray, atau laser

visible.

Laser dikatakan baik jika frekuensi atau panjang gelombang yang dipancarkannya

bersifat tunggal. Daya laser dapat dibuat bervariasi dari mulai nano watt untuk laser kontinyu

sampai triliunan watt untuk laser pulsa. Laser merupakan komponen utama pada sistem

komunikasi modern saat ini. Selain itu, laser juga dimanfaatkan sebagai probe untuk

pembacaan data CD atau DVD, sebagai sumber cahaya pada alat pembaca barcode, alat bantu

navigasi pada bidang militer, alat bantu operasi pada bidang kedokteran, dan masih banyak

lagi aplikasi lainnya.

Gambar

Bagan Laser

Peragaan peralatan Laser Helium-Neon di Laboratorium Kastler-Brossel

dariUniversitas Pierre and Marie Curie.

Beberapa kelebihan laser diantaranya adalah kekuatan daya keluarannya yang amat tinggi

sangat diminati untuk beberapa applikasinya. Namun demikian laser dengan daya yang

rendah sekalipun (beberapa miliwatt) yang digunakan dalam pemancaran, masih dapat

membahayakan penglihatan manusia, karena pancaran cahaya laser dapat mengakibatkan

mata seseorang yang terkena mengalami kebutaan dalam sesaat atau tetap.

Simbol laser untuk peringatan/pemberitahuan Sinar laser di atas kabut

udara dan di kaca mobil

DAFTAR KEKUATAN LASER DAN KEGUNAAN LASER

KEKUATAN KEGUNAAN / FUNGSINYA

1-5 mW Laser Penunjuk

5 mW Perangkat CD-ROM

5–10 mW DVD Player Atau Perangkat DVD-ROM

100 mW Kecepatan Tinggi Pembakaran Citra CD-RW

250 mW Pemakai Pembakaran DVD-R 16x

400 mW Membakar Kotak Perhiasan Dengan Diska Didalamnya Selama

4 Detik[3]

Percetakan DVD Piringan Ganda 24x[4]

1 W Laser Hijau Digunakan Didalam Piringan Holographic Versatile

Disc (HVD)

1–20 W Tidak Dijual Umum, Tetapi Ada Dan Digunakan Untuk Mesin

Kecil

30–100 W Pembedahan CO2

100–3000 W Pembedahan CO2 Dan Laser Ini Digunakan Untuk Pemotongan

Di Pabrik

5 kW Daya Pengeluarannya Mencapai 1 Cm/Bar

100 kW Digunakan Dalam Bidang Persenjataan Dan Didistribusikan

Oleh Northrop Grumman

Dalam banyak aplikasi, manfaat laser adalah karena sifat fisik mereka seperti

konsistensi, monochromaticity dan kemampuan untuk memperoleh kekuatan yang

sangat tinggi. Dengan contoh, sinar laser yang sangat koheren dapat difokuskan di

bawah batas difraksi pada panjang gelombang terlihat, yang hanya beberapa nanometer.

Ketika memfokuskan sinar laser yang kuat pada suatu titik, ia akan menerima

kepadatan tinggi. Penggunaan laser untuk merekam gigabyte informasi dalam rongga

mikroskopis dari CD, DVD atau Blu-ray. Hal ini juga memungkinkan media laser

memiliki intensitas rendah dalam mencapai daya yang sangat tinggi dan

menggunakannya untuk memotong, membakar atau sublimasi materi / objek / benda.

Laser banyak digunakan di dunia komunikasi, perbankan, kesehatan,

industri manufaktur, elektronika, instrumentasi iptek, sistem pengaman bank dan

gedung, sampai sistem militer. Bahkan grup musik, seperti Pink Floyd, Aerosmith,

dan Metallica, ikut-ikutan menggunakan laser dalam pertunjukan musiknya.

Dunia film pun sering menggunakan laser, biasanya sebagai sistem pengaman

yang otomatis menyalakan alarm saat ada penerobos tak diundang seperti dalam

salah satu adegan film Entrapment (Gambar 1).

Apa sebenarnya yang menjadi rahasia sukses laser? Apa keistimewaannya?

Apa yang membedakan sinar laser dengan sinar lampu senter biasa?

Gambar 1 Penerobos yang berusaha masuk harus menghindari laser

Tidak banyak yang tahu bahwa LASER sebenarnya merupakan singkatan

dari Light Amplification by Stimulated Emission of Radiation. Apa maksudnya ini?

Supaya bisa mengerti lebih jelas, terlebih dahulu kita harus memahami atom.

Atom

Sebuah atom terdiri dari inti atom yang disebut nukleus (berisi proton dan

netron), dan awan elektron (Gambar 2). Elektron-elektron ini selalu berputar

mengelilingi inti atom pada orbit-orbit tertentu, sesuai dengan tingkat energinya.

Dari sini kita tahu bahwa atom selalu bergerak (vibrasi dan rotasi), hanya saja kita

tidak bisa melihat pergerakannya di benda-benda padat seperti pintu, kursi, dan

semua benda lain. Jadi, benda yang selama ini kita kira dalam keadaan diam

sebenarnya tidak diam sama sekali!

Gambar 2 Ilustrasi sederhana sebuah atom

Orbit elektron yang memiliki tingkat energi paling rendah adalah yang

paling dekat dengan inti. Jadi, semakin jauh elektron dari inti, semakin tinggi pula

tingkat energinya. Ini artinya, kalau kita memberikan energi pada atom (misalnya

dalam bentuk energi panas, energi listrik, atau energi cahaya) maka elektron yang

berada di tingkat energi dasar (ground-state energy level) dapat tereksitasi (pindah)

ke orbit yang tingkat energinya lebih tinggi.

Lalu apa hubungannya dengan teknologi laser?

Gambar 3 Eksitasi elektron ke tingkat energi yang lebih tinggi

Emisi Cahaya Untuk Melepaskan Kelebihan Energi

Elektron yang sudah pindah ke tingkat energi yang lebih tinggi ini (excited

electron) berada dalam keadaan tidak stabil. Elektron ini selalu berusaha untuk

kembali ke keadaan awalnya dengan cara melepaskan kelebihan energi tersebut.

Energi yang dilepaskan berbentuk foton (energi cahaya) yang memiliki panjang

gelombang tertentu (warna tertentu) sesuai dengan tingkat energinya. Ini yang

disebut radiasi atom. Pada lampu senter ataupun lampu neon biasa, cahaya yang

dihasilkan menuju ke segala arah dan memiliki bermacam panjang gelombang dan

frekuensi (incoherent light). Hasilnya adalah cahaya yang sangat lemah.

Gambar 4

Kembalinya elektron ke tingkat energi semula disertai emisi cahaya

Pada teknologi laser, cahaya yang dihasilkan mempunyai karakteristik

tersendiri: monokromatik (satu panjang gelombang yang spesifik), koheren (pada

frekuensi yang sama), dan menuju satu arah yang sama sehingga cahayanya

menjadi sangat kuat, terkonsentrasi, dan terkoordinir dengan baik.

Bagaimana cara mengontrol emisi cahaya ini? Dengan menggunakan

bantuan cermin! Pada Gambar 5 kita melihat dua buah cermin yang diletakkan di

kedua ujung batu ruby. Salah satu cermin dibuat half-silvered (hanya

memantulkan sebagian cahaya; sementara cahaya yang tidak dipantulkan dapat

menerobos keluar). Ruby diberi stimulasi energi (disinari dengan cahaya)

sehingga beberapa elektronnya tereksitasi. Kemudian elektron yang tereksitasi ini

berusaha kembali ke tingkat energi awal dengan melepaskan cahaya (foton).

Cahaya ini memantul-mantul pada permukaan cermin dan menyinari elektron-elektron

‘tetangga’nya sehingga menyebabkan tereksitasinya para elektron

‘tetangga’ tersebut. Elektron-elektron ini kemudian juga mengemisikan cahaya

untuk kembali ke keadaan normalnya. Begitu seterusnya! Seperti reaksi berantai!

Sebagian cahaya berhasil menerobos keluar dari half-silvered mirror.

Sinar ini merupakan sinar yang monokromatik, koheren, dan berfasa tunggal

(single phase). Sinar inilah yang kita kenal sebagai sinar laser.

Gambar 5 Teknologi Laser

Ada bermacam media yang dapat digunakan untuk menghasilkan sinar

laser, misalnya solid state laser (menggunakan bahan padat sebagai medianya;

contoh: batu ruby), dan gas laser (misalnya gas helium, neon, CO2). Kekuatan

laser sangat bervariasi, bergantung pada panjang gelombang yang dihasilkannya.

Sebagai perbandingan, panjang gelombang yang dihasilkan ruby laser adalah 694

nm (6,94x10-7 m), sedangkan panjang gelombang yang dihasilkan gas CO2 adalah

10.600 nm (1,06x10-5 m). Batu ruby (CrAlO3) menghasilkan sinar laser berwarna

merah, sedangkan gas CO2 menghasilkan sinar pada daerah inframerah dan

gelombang mikro (microwave). Radiasi inframerah berbentuk panas sehingga

laser yang dihasilkan mampu melelehkan benda apa pun yang terkena sinarnya,

bahkan bisa digunakan untuk memotong baja!

Sinar laser yang berwarna-warni dihasilkan dari medium yang memiliki

panjang gelombang berbeda-beda. Biasanya laser yang berwarna-warni ini relatif

tidak berbahaya karena berada pada panjang gelombang yang relatif kecil. Warnawarni

indah laser ini dimanfaatkan untuk mempermanis pertunjukan musik

maupun acara-acara besar seperti perayaan menyambut tahun baru. Operasioperasi

kesehatan dan kecantikan juga memanfaatkan kedahsyatan sinar laser ini

karena mampu ‘menembak’ tepat pada target. Dalam dunia sehari-hari kita juga

bisa menemukan laser yang digunakan untuk barcode scanning di supermarket,

laser printer, CD (compact disc) player, dan yang paling umum adalah laser

pointer yang digunakan saat presentasi. Semua kecanggihan ini merupakan

tanggung jawab satu konsep sederhana fisika yang asyik dan

menyenangkan.(Yohanes Surya).

Gambar 6 Pertunjukan laser Infinity 2000 di Kunming Tower, Cina

BAB IV

PENUTUP

DAFTAR PUSTAKA

http://www.yohanessurya.com/Teknologi_18

http://id.wikipedia.org/wiki/Laser

Sumber: http://id.shvoong.com/exact-sciences/physics/2285157-pengertian-laser-dan-

definisi-laser/#ixzz1wRuDv7iO