Minia Universty FUCULTY OF ENGINEERING

ELECTRICAL ENGINEERING DEPARTMENT

GENERAL AND SCIENTIFIC USES OF LASER

Eng.Ahmed Sakr

LIST OF FIGURES:

Serial Title Page

1 Laser History 2

2 Laser production process 4

3 HeNe Laser device. 5

4 Laser diode and monitor photodiode arrangement in can-style package. 6

5 laser emission vs. wavelengths for laser and ordinary light 7

6 Divergence of Conventional Light Source 8

7 laser directional property 8

8 show the incoherent ordinary light and the coherence of laser. 9

9 Fiber Optic-communication cable 12

10 Using laser in PCB industry 14

11 Metal shaping using Laser. 15

12 Bending mechanism using laser. 17

13 Laser distance measurement 18

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Contents

TitleList of figuresAbstractIntroductionCHAPTER I:LASER DISCOVERY AND TYPES OF LASER

I.1. LASER DISCOVERY I.1.1. Relativity prediction of Laser.I.1.2. History of Laser sources.

I.2. Types of LASER I.2.1. solid state Laser.I.2.2. Gas Laser.I.2.3. Liquid Laser.I.2.4. Semiconductor Laser.

I.3. LASER CHARACTERISTICI.3.1. MONOCHROMATIC

I.3.2. DIRECTIONAL

I.3.3. COHERENT

CHAPTER II: LASER USES IN ENGINEERING II.1. COMMUNICATION SYSTEMS.

II.1.1. FIBER OPTIC-COMMUNICATION.II.1.2. SATELLITE COMMUNICATION AND GPS.

II.2. ELECTRICAL ENGINEERING.II.2.1.PRINTED CIRCUIT BOARD (PCB).

II.2. INDUSTRY.II.2.1.SHEET METAL SHAPING.

II.2.1.1.CUTTING.II.2.1.2.BENDING.

II.3. CIVIL ENGINEERING.II.3.1 DISTANCE MEASUREMENT.

CHAPTER III: LASER USES IN MEDICINEIII.1. OPHTHALMOLOGY.III.2.CANCER.III.3. COSMETIC LASER SURGERY.

CHAPTER IV: LASER USES IN NUCLEAR ENERGY SCIENCE IV.1. ENRICHMENT.IV.2. FUSION REACTORS.

CHAPTER V: LASER USES IN ASTRONOMYV.1.MAPPING THE EARTH.V.2.MAPPING THE MOON.

REFERENCES

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ABSTRACT

Laser is the most well known scientific discovery in the world. Because of its special characteristics, it has many uses in approximately all live fields. The first laser source was created by Theodore Maiman on 16th May 1960. Since that date, Laser joined all the fields we know. You will find a lot of uses of laser in engineering, medicine, astronomy, nuclear power and energy science etc.

Our study includes the history of laser since Einstein’s prediction of it, through Maiman’s first Laser source and the discovery of all laser types we know. Then we will cover the most common uses of laser in: Engineering (as in Communication Systems, Industry, Mapping, and PCB manufactory). Medicine (as Ophthalmology, Cancer, and Cosmetic Laser Surgery), Nuclear energy science, and Astronomy.

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Introduction:

Albert Einstein established the theoretic foundations for the LASER. On 16th May 1960, Theodore Maiman demonstrated the first functional laser capable of producing short pulses. There are many types of Laser Like solid state Laser, Gas Laser, Semiconductor Laser, and Liquid Laser. Laser characteristics are Monochromatic, Directional, and Coherent.

Laser is critical for engineers. They use it in many branches of engineering .In communication systems it is used in F.O.C. and satellite communication. In electrical engineering it is used for manufactory of Printed Circuit Board. in industry, laser has many uses like sheet material treatment like Cutting and bending. And Civil engineers use Laser in distance measurements.

Another field that uses laser is medicine. It is used in ophthalmology (eye disease), Cancer and Tumors, and Cosmetic.

Laser is sharply used in nuclear energy science as in Fusion Reactors and enrichment. Energy is delivered to the outer layer of the target in fusion reactors using high-energy beams of laser light.

We can’t neglect the useful usage of laser in astronomy. NASA uses Laser in most of its work and researches. The most recent use of laser in astronomy and geometry is mapping Earth and Moon using Laser satellites.

Laser is used also in many other fields like agriculture, plastic industry, decoration, and many other purposes.

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CHAPTER I

LASER DISCOVERY AND TYPES OF LASER

I.1. LASER DISCOVERY

I.1.1. RELATIVITY’S PREDICTION OF LASER.I.1.2. HISTORY OF LASER SOURCE.

I.2. TYPES OF LASER

I.2.1. SOLID STATE LASER.I.2.2. GAS LASER.I.2.3. LIQUID LASER.I.2.4. SEMICONDUCTOR LASER.

I.3. LASER CHARACTERISTIC

I.3.1. MONOCHROMATIC

I.3.2. DIRECTIONAL

I.3.3. COHERENT

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Fig.1: Laser History

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I.1. LASER DISCOVERY

I.1.1. Relativity prediction of Laser.

In 1917, Albert Einstein established the theoretic foundations for the LASER 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. In 1939, Valentine A. Fabrikant predicted the use of stimulated emission to amplify “short” waves .In 1947, Willis E. Lamb and R. C. Rutherford found apparent stimulated emission in hydrogen spectra and effected the first demonstration of stimulated emission .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.

I.1.2. History of Laser sources.

On 16 May 1960, Theodore Maiman demonstrated the first functional laser capable of producing short pulses. He used a solid-state flash lamp-pumped synthetic ruby crystal to produce red laser light, at 694 nanometers wavelength.

Later in 1960, the Iranian physicist Ali Javan, and William R. Bennett, and Donald Herriot, constructed the first gas laser, using helium and neon that was capable of continuous operation.

In 1962, Nick Holonyak, Jr. demonstrated the first semiconductor laser with a visible emission. Like the early gas laser device, the early semiconductor laser could only be used in pulsed-beam operation, and when cooled to liquid nitrogen temperatures (77˚K).

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I.2. Types of LASER

Here, we will classify laser types by the medium material type. For example, the solid state laser is that type of laser we use a SOLID mid. Material.

I.2.1. solid state Laser.

The first laser source created by Maiman was a solid state laser. The first material used for lasing was ruby. Ruby lasers are still used for some applications, but are not common due to their low

efficiency.

Fig.2: Laser production process

Now, we use other materials to product the Solid-state Laser, like ytterbium-doped glasses and ceramics.

Another type of solid-state laser is the semiconductors laser which we will talk about later.

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I.2.2. Gas Laser.

It is the laser in which the active medium is a gas containing a laser active species. It is typically composed of a plasma discharge tube containing a gas that can be excited with an electric discharge. [1]

The first gas laser used a combination of helium and neon as an active medium. Now other gases are used to produce laser like Nitrogen laser, Carbon dioxide laser, Ion laser and Gas dynamic laser[2].

Fig.3: HeNe Laser device.

I.2.3. Liquid Laser.

It is a laser in which a liquid solution is the active species. [3]

Common liquid which is used in this type of laser is CF3I.

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I.2.4. Semiconductor Laser.

The commercial and industrial use of laser diodes has dramatically increased with some common applications such as barcode scanning and fiber optic communications. The optical characteristics, small size, and ruggedness of laser diodes have allowed many new uses to be commercialized.

Fig. 4: Laser diode and monitor photodiode arrangement in can-style package.

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I.3. LASER CHARACTERISTIC

I.3.1. MONOCHROMATIC

Monochromatic means that it consists of one single color or wavelength. Even through some lasers can generate more than one wavelength, the light is extremely pure and consists of a very narrow spectral range.

Fig.5: Nearly 100% of the laser emission act in a narrow range of wavelengths [790:820] nm. The 2nd plot shows the emission of ordinary xenon lamp which act in a very wide range of wavelength [0:1500] nm.

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I.3.2. DIRECTIONAL

Directional means that the beam is well collimated (very parallel) and travels over long distances with very little spread. The angle of divergence of the laser beam is too small.

Fig.6: Divergence of Conventional Light Source

The output of a laser has a very small divergence and can maintain high beam intensities over long ranges.  Thus, relatively low power lasers are able to project more energy at a single wavelength within a narrow beam than can be obtained from much more powerful conventional light sources.

Fig.7 : laser directional property

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I.3.3. COHERENT

Coherent means that the waves of light are in phase with each other.  A light bulb produces many wavelengths, making it incoherent.

Fig.8: Left image shows the incoherent ordinary light. Right image shows the coherence of laser.

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CHAPTER II

LASER USES IN ENGINEERING

II.1. COMMUNICATION SYSTEMS.

II.1.1. FIBER OPTIC-COMMUNICATION.

II.1.2. SATELLITE COMMUNICATION AND GPS.

II.2. ELECTRICAL ENGINEERING.

II.2.1.PRINTED CIRCUIT BOARD (PCB).

II.2. INDUSTRY.

II.2.1.SHEET METAL SHAPING.

II.2.1.1.CUTTING.

II.2.1.2.BENDING.

II.3. CIVIL ENGINEERING .

II.3.1 DISTANCE MEASUREMENT.

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II.1. COMMUNICATION SYSTEMS .

Before the invitation of laser, the common method that was used for transfer information in using telegram or metal cables .That had a lot of disadvantages like lose of data and noise.

Laser make it more comfortable to transfer data without noise and with minimum data lose as one of its characteristics is Directional

II.1.1. FIBER OPTIC-COMMUNICATION.

One of the most common communication methods is the F.O.C. It uses fiber glass to transfer information between Sender and Receiver. First it in-code information to [0,1] (Binary system) using electronic circuits .Then, it uses the semiconductor laser to transmit the in-coded information through the Fiber Glass cable .Finally , the laser beam is collected and analyzed using another electronic circuit to use the information the laser beam carries.

This method is used instead of the metal cable because it gives high speed, low noise and low cost as it uses fibers made of glass which is not expensive.

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Fig.9: Fiber Optic-communication cable

II.1.2. SATELLITE COMMUNICATION AND GPS.

Significant development and implementation of the satellite communications infrastructure has occurred over the past five decades. As the United States Military expands its role in the war on terror across the globe, the strain on the communications infrastructure to meet the requirements of commercial and military communications applications increases and adversely affects currently deployed national assets. As the demand for scalable, secure, high capacity, high data rate Free-Space Optical (FSO) communication links increases beyond the capability of traditional radio frequency (RF) systems, satellite laser communication systems provide an effective alternative to its RF counterparts.

Inherent in the design of control systems used for pointing, such as that used for the Transformational Communications Satellite (TSAT),

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is the ability to provide specific information regarding the position and attitude of a node in a satellite constellation. Combining this with relative range measurements allows complete determination of relative position of the node. This may be extended further by associating platforms with simultaneous access, such as those technologies incorporated in the design of the Multi-Access Laser Space Terminal (MALST). The incorporation of techniques that process laser communication pointing control system measurements to produce relative attitude and range estimates would facilitate the improvement of fault tolerances and allow for simpler orbital control systems and inertial measurement units (IMUs) to be implemented in the system design [10].

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II.2. ELECTRICAL ENGINEERING.

II.2.1.PRINTED CIRCUIT BOARD (PCB).

The increasing demands for miniaturization and better functionality of electronic components and devices have a significant effect on the requirements facing the printed circuit board (PCB) industry. PCB manufactures are driving for producing high density interconnect (HDI) boards at significantly reduced cost and reduced implementation time. The interconnection complexity of the PCB is still growing and today calls for 50/50 μm or 25/25 μm technology are real. Existing technologies are unable to offer acceptable solution. Recently the Laser Direct Imaging (LDI) technology is considered as an answer for these challenges. LDI is a process of imaging electric circuits directly on PCB without the use of a photo tool or mask. Our laboratory system for Laser Direct Imaging is designed for tracks and spaces on PCB with minimum width distance of 50/50 μm. In comparison with conventional photolithography method, this technology is much better for 50/50 μm track and spaces. In our research we used photo resist with resolution 50 μm, but in case of using laser photo resists with better resolution (e.g. 25 μm) it will be possible to image tracks in super-fine-line technology (25/25 μm). The comparison between two technology of creating mosaic pattern tracks on PCB proved that laser imaging is promising technology in high density interconnects patterns, which are widely use in multilayered PCB and similar applications [11].

Fig.10: Using laser in PCB industry.

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II.2. INDUSTRY.

II.2.1.SHEET METAL SHAPING.

Laser forming is an emerging rapid prototyping (RP) technique that has undergone research worldwide since the mid 1980s. It is a thermo-mechanical process whereby the localized heat input of the laser induces compressive stresses within the material causing it to bend. The process belongs under the umbrella of CAD/CAM technologies, since software can be used to convert a CAD drawing into the data required to drive the axes.

II.2.1.1.CUTTING.

The laser beam is a multi-functional tool. Its strength is made up by the possibility of working with completely different materials, both of thin or thick dimensions. For example, the operation of boring holes in very thick materials, which by using traditional shearing methods would create the inevitable breakage of the cutting tools, are carried out without difficulty with laser cutting technology.

Fig.11: Metal shaping using Laser.

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The laser cutting system which operates on 5 axes with an internal beam track, allows for the sheet metal to be cut even after having been shaped by the drawing process. This allows for the production of particular pieces which in the past remained solely ideal projects on paper, as they were impossible to realize with traditional technology.

By using traditional mechanical technology, this type of operation was only possible with extremely high production costs.

Three steps can be distinguished in this process. In a first stage, powerful algorithms are used to generate good nestings while minimizing the waste material. Next, the laser cutting technology such as cutting speed, piercing method, lead-in etc. is selected. Finally, the cutting path is optimized, taking into account cutting distance minimization, best cutting direction and lowest heat build-up[4].

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II.2.1.2.BENDING.

Starting with a piece of sheet metal of large dimensions going to a precision piece of a complex shape, the folding presses in the Laser Tech department offer various opportunities of usage from coinage to the bending of sheet metal, from thin to very thick materials.These machines, controlled by numerical checking, operate quickly and are used in both an economical and productive way in various applications.

Fig.12: Bending mechanism. Each method is determined by the gradient of compression that is created by the distribution of heat through the metal [5].

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II.3. CIVIL ENGINEERING.

II.3.1 DISTANCE MEASUREMENT.

To measure distances with lasers or laser scanners is well established - you will find this technique in geodesic systems, security systems, production control systems and even with golfplayers. Different methods are available. Small distances are measured by triangulation. Using this method the achieved resolution will be in the range of micrometers, but the maximumrange is limited to only a few meters. Up to distances of 100m people often use the phase shift measurement. The laser light is modulated and the phase-shift between outgoing and incominglight gives the distance. To reach a resolution in the millimeter range very high sampling rates are necessary. Only low measuring rates with high current consumption are possible theConsequence [6].

Usually the ray of light will be reflected at an object or mirror. Therefore the light passes the distance twice. So we will have:1ns - 150mm distance (reflection)100ps - 15mm ’’10ps - 1,5mm ’’.

Fig.13: Laser distance measurement.

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CHAPTER III

LASER USES IN MEDICINE

III.1. OPHTHALMOLOGY.

III.2.CANCER.

III.3. COSMETIC LASER SURGERY.

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III.1. OPHTHALMOLOGY.

An increased understanding of laser-tissue interactions in ophthalmology has led to the use of lasers in treating a wide spectrum of diseases involving both the anterior and posterior segments of the eye. These diseases include the four commonest causes of blindness in the United States: diabetic retinopathy, age-related macular degeneration, glaucoma and cataract. As knowledge of the operating characteristics and treatment limitations of lasers increases, the use of lasers in the treatment of other ophthalmologic problems will be broadened [7a].

The use of lasers in ophthalmology has permanently altered the traditional ways of treating certain eye disorders. Invasive surgical intervention for some glaucomas and cataracts has been replaced by outpatient laser procedures. The visual prognosis for patients with diabetes mellitus has improved significantly with laser photocoagulation, and patients with treatable choroidal neovascular diseases have responded well to laser surgical techniques. Treatment of other retinal neovascular and abnormal vascular diseases with laser photocoagulation enjoys a high success rate. As continuing clinical research further defines the operating characteristics and indications for the use of existing and newer generations of lasers, ophthalmologists will be able to treat a broader spectrum of eye disease with greater precision and safety [7b].

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III.2.CANCER AND TUMORS.

Laser surgery, or laser-induced thermal therapy, is a minimally invasive alternative or adjuvant to surgical resection in treating tumors embedded in vital organs with poorly defined boundaries. Its use, however, is limited due to the lack of precise control of heating and slow rate of thermal diffusion in the tissue. Nanoparticles, such as nanoshells, can act as intense heat absorbers when they are injected into tumors. These nanoshells can enhance thermal energy deposition into target regions to improve the ability in destroying larger cancerous tissue volumes with lower thermal doses. The goal of this paper is to present an integrated computer model using a so-called nested-block optimization algorithm to simulate laser surgery and provides transient temperature field predictions. In particular, this algorithm aims to capture changes in optical and thermal properties due to nanoshell inclusion and tissue property variation during laser surgery. Numerical results show that this model is able to characterize variation of tissue properties for laser surgical procedures and predict transient temperature field comparable to that measured by in vivo magnetic resonance temperature imaging (MRTI) techniques. Note that the computational approach presented in the study is quite general and can be applied to other types of nanoparticle inclusions[8].

The extent of thermal damage associated with traditional laser therapies is limited by thermal diffusion in the tissue. Most conventional laser therapies, other than photodynamic therapy, do not permit selective destruction of tumor tissue while preserving the surrounding healthy tissue. In order to circumvent the limitations of traditional laser therapies employed in cancer treatment, nanoshells were employed to enhance the thermal deposition and selectivity of thermal damage.

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III.3. COSMETIC LASER SURGERY.

In recent years, lasers have shed their science fictional image to become a surgeon's and dermatologist's most promising weapon in the fight against aging skin. According to the American Academy of Cosmetic Surgery in Chicago, nearly 170,000 Americans, men and women, underwent laser resurfacing of the face in 1998, up from 138,891 in 1996, a 64 percent increase. That's nearly twice the number of the more traditional surgical facelifts performed in the same year.

Laser resurfacing is a very controlled burning procedure during which a laser vaporizes superficial layers of facial skin, removing not only wrinkles and lines caused by sun damage and facial expressions, but also acne scars, some folds and creases around the nose and mouth, and even precancerous and benign superficial growths. In a sense, the laser procedure creates a fresh surface over which new skin can grow.

While the Food and Drug Administration does not regulate how surgeons carry out these procedures, it is responsible for clearing lasers for marketing for the uses requested by the device's manufacturer.

Since their 1958 discovery, lasers have become a powerful industrial tool, but their applications in medicine have been truly revolutionary. One reason, says Richard Felten, a senior reviewer in FDA's Center for Devices and Radiological Health, is that lasers used as surgical tools can cut through tissue without causing excessive bleeding. In fact, lasers actually can coagulate tissue to stop bleeding. "That's something a knife can't do," Felten says. Also, for many internal procedures, surgeons can get the laser's energy to reach areas within the body more easily than with a scalpel. And finally, the wavelengths of the laser light itself lets surgeons use the device selectively on very specific types of tissues, such as port wine stains or hair follicles, without affecting nearby tissue [9]. 

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CHAPTER IV

LASER USES IN NUCLEAR ENERGY SCIENCE

IV.1. ENRICHMENT.

IV.2. FUSION REACTORS.

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IV.1. ENRICHMENT.

Enrichment is a process that increases the capacity of uranium to fuel a nuclear chain reaction, either for use in nuclear power plants or for nuclear weapons. Uranium primarily occurs naturally as two isotopes: 99.3% is Uranium-238 and 0.7% is Uranium-235. Their atoms are identical except for the number of neutrons in the nucleus. Uranium-238 has three more and this makes it less able to fission. Uranium enrichment is used to increase the percentage of the fissile U-235.Nuclear reactors typically require uranium fuel enriched to about 3% to 5% U-235. Nuclear bombs typically use ‘Highly Enriched Uranium’, enriched to 90% U-235, although lower levels of enrichment can be used.

There are a wide range of techniques for enriching uranium, all of which are based on using the slight differences between the heavier U-238 and U-235 to separate them. As a first step the uranium metal is turned into a gas (uranium hexafluoride, UF6). Methods which have been used include pumping the gas through membranes or nozzles, spinning it in centrifuges at speeds approaching the speed of sound, using slightly different chemical properties of the isotopes (caused by slight differences in the size of the atoms), and with lasers using different optical properties to create charged atoms or molecules by energizing some of their electrons. The most widely used is the centrifuge process, for producing both reactor grade and highly enriched uranium. In the 1960s and 70s Australia maintained a research program at Lucas Heights into centrifuge enrichment. Australia currently has a research and development program, whose details are classified, for laser enrichment called SILEX (Separation of Isotopes by Laser Excitation). It has recently been licensed to General Electric Energy where the company hopes to develop a demonstration pilot separation plant [12].

Laser processes promise lower energy inputs, lower capital costs and lower tails assays, hence significant economic advantages. Several laser processes have been investigated or are under development.

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None of the laser processes below are yet ready for commercial use, though SILEX is well advanced and expected to begin commercial production in 2012.

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IV.2. FUSION REACTORS.

Inertial confinement fusion (ICF) is a process where nuclear fusion reactions are initiated by heating and compressing a fuel target, typically in the form of a pellet that most often contains a mixture of deuterium and tritium.

To compress and heat the fuel, energy is delivered to the outer layer of the target using high-energy beams of laser light, electrons or ions, although for a variety of reasons, almost all ICF devices to date have used lasers. The heated outer layer explodes outward, producing a reaction force against the remainder of the target, accelerating it inwards and sending shock waves into the center. A sufficiently powerful set of shock waves can compress and heat the fuel at the center so much that fusion reactions occur. The energy released by these reactions will then heat the surrounding fuel, which may also begin to undergo fusion. The aim of ICF is to produce a condition known as "ignition", where this heating process causes a chain reaction that burns a significant portion of the fuel. Typical fuel pellets are about the size of a pinhead and contain around 10 milligrams of fuel: in practice, only a small proportion of this fuel will undergo fusion, but if all this fuel were consumed it would release the energy equivalent to burning a barrel of oil.

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CHAPTER V

LASER USES IN ASTRONOMY

V.1.MAPPING THE EARTH.

V.2.MAPPING THE MOON.

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V.1.MAPPING THE EARTH.

High resolution digital terrain models (DTMs) and digital surface models (DSMs) are critical for predicting flooding, monitoring erosion, landslide and tectonic movements, modeling ecosystems, and creating digital city models. Recently emerging airborne light detection and ranging (LIDAR) technology allows accurate and inexpensive measurements of topography, vegetation canopy heights, and buildings over large areas. In order to provide researchers with high quality data, NSF has created the National Airborne Laser Mapping Center (NCALM) to collect, archive, and distribute the LIDAR data. However, airborne LIDAR systems collect huge volumes of irregularly spaced, three-dimensional point measurements of ground and non-ground objects scanned by the laser beneath the aircraft. To advance the use of the technology and data, there is a need for basic research in algorithms for data retrieval and transformation, and ground and non-ground measurement classification. There is also a need for additional software which includes these algorithms and other basic data processing tools to help researchers to extract the desired information from airborne LIDAR data for their applications.In order to satisfy these needs, we have developed a set of transparent and automatic filtering algorithms to classify ground and non-ground LIDAR measurements and a series of auxiliary tools such as thinning, tiling, and gridding the point data sets to assist the LIDAR data analysis. A graphics-based user interface has also been developed to facilitate the usage of algorithms and tools. We hope that the algorithms and software will provide researchers with the necessary tools to analyze LIDAR data and derive useful information in order to understand and model natural and human-induced earthsurface processes and their changes. We also hope that the LIDAR data processing and analysis tools will help promote the scientific, government, and the public’s use of LIDAR data and technology to predict topographic effects of major earthquakes, large scale flooding, extensive landslides, and erosion. These algorithms and tools were developed through the cumulative efforts of the authors in airborne laser mapping research during the past eight years. We would like tothank NCALM and NOAA Florida Hurricane Alliance Research Program for providing the necessary financial support for this project[13].

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V.2.MAPPING THE MOON.

According to NASA's Vision for Space Exploration, astronauts will return to the Moon as early as 2015. This is a key step en route to Mars and beyond. On the Moon, which is practically in Earth's backyard, astronauts can learn how to live on an alien world before attempting longer voyages to other planets.

However, our current maps of the Moon are not very precise. In some areas, near Apollo landing sites, for instance, the locations of craters and ridges are well known. They were extensively photographed by lunar orbiters and Apollo astronauts. But much of the lunar surface is known only approximately.

"If you ask 'where is a crater on the far side of the Moon?', chances are there's probably many kilometers of uncertainty in its true positioning," says David Smith, a scientist at NASA's Goddard Space Flight Center. Even on the near side of the Moon, Smith adds, errors in the true global position of features may be as large as a kilometer.

To improve this situation, NASA plans to send a high-precision laser altimeter to orbit the Moon and create a 3-dimensional map of its surface. When completed, the map will be so accurate that we'll know the contours of the Moon better than we do some remote regions on Earth. Astronauts will be able to use it like a USGS hiking map.

The laser is named "LOLA," short for Lunar Orbiter Laser Altimeter. It's scheduled to launch in 2008 onboard the Lunar Reconnaissance Orbiter spacecraft. LOLA works by bouncing pulses of laser light off the lunar surface as it orbits the Moon. By measuring the time it takes for light to travel to the surface and back, LOLA can calculate the roundtrip distance. LOLA is capable of timing pulses with a precision of 0.6 nanoseconds, corresponding to a distance error of no more than 10 cm.

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13. Keqi Zhang and Zheng Cui,”Airborne LIDAR Data Processing and Analysis Tools”, National Center for Airborne Laser Mapping, USA, P.1, 2007.

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