Introduction to Nitride Semiconductor Blue Lasers and Light Emitting Diodes 0748408363
Introduction to Lasers
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Transcript of Introduction to Lasers
Las rsIntroduction to
e
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• Laser Applications
• Definition of lasers
• Population Inversion
• Materials used for semiconducting laser
• Quantum dot devices
• Laser Safety
lasersIntro to
Lecture Contents
lasersIntro to
TELECOMMUNICATION
Laser Applications
FLAG network(Fiber-optic Link Around the Globe)
Flag Network Collaboration In India
Reliance Communications
10 Gbits /s
From UK to Japan
Flag Network owned by
Reliance Globecom -UK
28OOOKM
Another Typical Application of
• An example of application is for the light source for fibre optics communication.
• Light travels down a fibre optics glass at a speed, = c/n, where n = refractive index.
• Light carries with it information• Different wavelength travels at different speed. • This induce dispersion and at the receiving end the light is
observed to be spread. This is associated with data or information lost.
• The greater the spread of information, the more loss• However, if we start with a more coherent beam then loss can
be greatly reduced.
lasersIntro to
Laser – Fibre Optics
lasersIntro toLaser Applications
# The liver and lung diseases could be
treated using lasers.
Lasers are used extensively
in the treatment of
eye-diseases ,particularly to
reattach a detached retina.
MEDICINAL PURPOSE
Bloodless Surgery.
Fiber optic
Endoscopeto
Detect ulcers
in the intestines.#
lasersIntro toLaser Applications
MEDICINAL PURPOSE
• To destroy cancerous and precancerous cells; at the same
time, the heat seal off capillaries,
To remove plaque clogging
human arteries
To break up gallstones and
kidney stones
lasersIntro toLaser Applications
# For precision measurements & leveling
Laser light is used to collect the
information about the prefixed prices of
various products in shops and
business establishments from the bar-
code printed on the product.
INDUSTRIAL PURPOSES
lasers are used now for cutting, drilling and
welding of metals and other materials.
#
• LIDAR –Light Detection & Ranging (Mines)
• Leveling of Ceramic Tile Floor
lasersIntro toLaser Applications
INDUSTRIAL PURPOSES
Milling tool3D printers Latching tool
A variety of 3D printing techniques have appeared in the last few years.
SLA: Stereolithography: laser curing of liquid plastic.
SLS: Selective Laser Sintering: similar, laser fuses powder.
LOM: Layered Object Modeling: laser cuts paper one layer at a time.
FDM: Fused Deposition Modeling: a thread of plastic is melted through a
moving head.
PC-board CAD tools s
lasersIntro toLaser Applications
# In sniper guns, for target acquisition & locking
Dragunov SVD – Semi Automatic Sniper gun
LASTEC- HPL Researches(Laser Science & Technology Centre)
Under DRDO
DEFENCE & SECURITY
Indian ARM industry :- OFB (Ordinance Factories Board )
(Defence Research & Development Organisation)
#
lasersIntro to
• Laser guided munitions– Designated from air or ground
• Thermal homing missiles
• Optical Guidance
• Night Vision
MILITARY USES
THERMAL IMAGING THERMAL IMAGING
Lasers – Military Applications
• Targeting tool
– Absorbed by target – thermal radiator
– Reflected by target – selective radiator
• Modulated
– Different lasers of the same frequency to be deconflicted and
limits enemy interference
• Weapon Systems: Hellfire, Maverick, Rockeye
• Laser Range finders, Beam riders, and laser target
designators (LTD)
• THEL & MHEL - Tactical High Energy Laser (Shoot down
incoming)
lasersIntro to@ www.gizmag.com/millitarygadgets
• Holography is the production of holograms by the use of laser.
Laser ApplicationsHOLOGRAPHY
lasersIntro to
@ www.pranavmistry.com
• Possible medical applications using the technology– Surgical procedures (using tracking capabilities)
– Rehabilitation techniques & Gaming
Laser ApplicationsHOLOGRAPHY
lasersIntro to
Typical Application of Laser
The detection of the binary data stored in the form of pits on
the compact disc is done with the use of a semiconductor
laser. The laser is focused to a diameter of about 0.8 mm at
the bottom of the disc, but is further focused to about 1.7
micrometers as it passes through the clear plastic substrate
to strike the reflective layer. The reflected laser will be
detected by a photodiode. Moral of the story: without
optoelectronics there will no CD player!
lasersIntro to
Light
Amplification by
Stimulated
Emission of
Radiation
BASIC LASER
lasersIntro to
• A laser is a device that generates light by a processcalled STIMULATED EMISSION.
• The acronym LASER stands for Light Amplificationby Stimulated Emission of Radiation
• Semiconducting lasers are multilayer semiconductordevices that generates a coherent beam ofmonochromatic light by laser action. A coherentbeam resulted which all of the photons are inphase.
Definition of
laser
lasersIntro to
10-13 10-12 10-11 10-10 10-9 10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1 1 10 102
LASERS
200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 10600
Ultraviolet Visible Near Infrared Far Infrared
Gamma Rays X-Rays Ultra- Visible Infrared Micro- Radar TV Radio
violet waves waves waves waves
Wavelength (m)
Wavelength (nm)
Nd:YAG
1064
GaAs
905
HeNe
633
Ar
488/515
CO2
10600
XeCl
308
KrF
248
2w
Nd:YAG
532
Retinal Hazard Region
ArF
193Communication
Diode
1550
Ruby
694
Alexandrite
755
Electromagnetic Spectrum
lasersIntro toLasers operate in the ultraviolet, visible, and infrared.
• Monochromaticity– Laser light is concentrated in a narrow range of wavelengths
• Coherence– All the emitted photons bear a constant phase relationship with
each other in both time and phase
• Directionality– laser light is usually low in divergence
• High Irradiance– Power of EM radiation Incident per unit area
Properties of Laser Light
lasersIntro to
Diode Laser
lasersIntro to
Neodymium Yag Laser
Types of LASERS LASERS
Solid state Liquid Gas Lasers
Semiconductor
Solid state Liquid
Gaseous
Ruby laser
Market demand of QD lasers
QD Lasers
Microwave/Millimeter wave
transmission with optical fibers
Da
tac
om
ne
two
rk
Te
lec
om
ne
two
rk
Optics
( QUANTUM DOT )
High speed QDL Advantages
Directly Modulated Quantum Dot Lasers
•Datacom application
•Rate of 10Gb/s
Mode-Locked Quantum Dot Lasers
•Short optical pulses
•Narrow spectral width
•Broad gain spectrum
•Very low α factor-low chirp
InP Based Quantum Dot Lasers
•Low emission wavelength
•Wide temperature range
•Used for data transmissionlasersIntro to
@ www.fibers.org
DEFINITION OF MPE
The level of laser light to which a person may be
exposed without risk of injury.
lasersIntro to
For atomic systems in thermal equilibrium with their surrounding,
the emission of light is the result of:
Absorption
And subsequently, spontaneous emission of energy
There is another process whereby the atom in an upper energy level can
be triggered or stimulated in phase with the an incoming photon. This
process is:
Stimulated emission
It is an important process for laser action
Therefore 3 process of
light emission:
Mechanisms of Light Emission
1. Absorption
2. Spontaneous Emission
3. Stimulated Emission
Stimulated Emission
•It is pointed out by Einstein that:
“Atoms in an excited state can be stimulated to jump to a
lower energy level when they are struck by a photon of incident light
whose energy is the same as the energy-level difference involved in
the jump. The electron thus emits a photon of the same wavelength as
the incident photon. The incident and emitted photons travel away
from the atom in phase.”
This process is called stimulated emission. lasersIntro to
Excited
electron
Unexcited
electron
Before emission After emission
Stimulated EmissionlasersIntro to
Incident
photon Incident
photon
Emitted
photon
In order to obtain the coherent light from stimulated emission,
two conditions must be satisfied:
1. The atoms must be excited to the higher state. That is, an
inverted population is needed, one in which more atoms are
in the upper state than in the lower one, so that emission of
photons will dominate over absorption.
Unexcited system
1E
2E3E
Excited system
1E
2E3E
lasersIntro to
2. The higher state must be a metastable state – a state in which the
electrons remain longer than usual so that the transition to the
lower state occurs by stimulated emission rather than
spontaneously.
Metastable state
Photon of energy12 EE
1E
2E
3E
Metastable system
1E
2E
3E
Stimulated emission
Incident photon
Emitted photon
Metastable StatelasersIntro to
Common Laser System
lasersIntro to
BASIC LASER COMPONENTSACTIVE MEDIUM
Solid (Crystal)
Gas
Semiconductor (Diode)
Liquid (Dye)
EXCITATION
MECHANISM
Optical
Electrical
Chemical
OPTICAL
RESONATOR
HR Mirror and
Output Coupler
The Active Medium contains atoms which can emit light
by stimulated emission.
The Excitation Mechanism is a source of energy to
excite the atoms to the proper energy state.
The Optical Resonator reflects the laser beam through
the active medium for amplification.
High ReflectanceMirror (HR)
Output CouplerMirror (OC)
ActiveMedium
Output
Beam
Optical Resonator
lasersIntro to
Excitation Mechanism
Laser Wavelength Linewidth
lasersIntro to
CDRH CLASS WARNING LABELS
CLASS II LASER PRODUCT
Laser RadiationDo Not Stare Into Beam
Helium Neon Laser
1 milliwatt max/cw
CLASS IV Laser Product
VISIBLE LASER RADIATION-
AVOID EYE OR SKIN EXPOSURE TO
DIRECT OR SCATTERED RADIATION
Argon Ion
Wavelength: 488/514 nm
Output Power 5 W
Class II
Class IIIa with expanded beam
Class IIIa with small beam
Class IIIb
Class IV
lasersIntro to
INTERNATIONAL LASER WARNING LABELS
Symbol and Border: Black
Background: Yellow
Legend and Border: Black
Background: Yellow
INVISIBLE LASER RADIATION
AVOID EYE OR SKIN EXPOSURE
TO DIRECT OR SCATTERED RADIATION
CLASS 4 LASER PRODUCT
WAVELENGTH 10,600 nm
MAX LASER POWER 200 W
EN60825-1 1998
lasersIntro to
Courtesy of Los Alamos National Laboratory
NEODYMIUM YAG LASERlasersIntro to
Rear Mirror
Adjustment Knobs
Safety Shutter Polarizer Assembly (optional)
CoolantBeamTube
AdjustmentKnob
OutputMirror
Beam
Beam Tube
HarmonicGenerator (optional)
Laser Cavity
PumpCavity
Flashlamps
Nd:YAGLaser Rod
Q-switch(optional)
Medium :- Neodymium-Doped Yttrium Aluminum Garnet Crystal
State :- Solid
Excitation :- Diode Laser
Beam :- 1064 nm infrared
Uses :- Cataract ,Glaucoma , Gingivectomy surgeries
Light Absorption• Dominant interaction
– Photon absorbed
– Electron is excited to CB
– Hole left in the VB
• Depends on the energy band gap (similar to lasers)
• Absorption (a) requires the photon energy to be larger than the material band gap gE
hc
) )m
eVEE
hc
gg
24.1
lasersIntro to
LASER HAZARD CLASSES
Lasers are classified according to the level of laser radiation that
is accessible during normal operation.
lasersIntro to
CLASS 1• Safe during normal use• Incapable of causing injury• Low power or enclosed beam
CLASS I Laser Product
Label not required
May be higher class duringmaintenance or service
Nd:YAG Laser Marker
CLASS 2
CLASS II LASER PRODUCT
Laser RadiationDo Not Stare Into Beam
Helium Neon Laser1 milliwatt max/cw
• Staring into beam is eye hazard
• Eye protected by aversion response
• Visible lasers only
• CW maximum power 1 mW
Laser Scanners
CLASS 3R (Formerly 3a)
Small Beam
Expanded Beam
CLASS IIIa Laser Product
LASER RADIATION-
AVOID DIRECT EYE EXPOSURE
ND:YAG 532nm
5 milliwatts max/CW
• Aversion response may not provide
adequate eye protection
• CDRH includes visible lasers only
• ANSI includes invisible lasers
• CW maximum power (visible) 5 mW
Laser Pointers
CLASS IIIa LASER PRODUCT
Laser Radiation-Do Not Stare Into Beam or ViewDirectly With Optical Instruments
Helium Neon Laser5 milliwatt max/cw
CLASS 3B
• Direct exposure to beam is eye hazard
• Visible or invisible
• CW maximum power 500 mW
CLASS IIIb Laser Product
LASER RADIATION-
AVOID DIRECT EXPOSURE TO BEAM
2w ND:YAG Wavelength: 532 nm
Output Power 80 mW
Courtesy of Sam’s Laser FAQ, www.repairfaq.org/sam/lasersam.htm, © 1994-2004
DPSS Laser with cover removed
CLASS 4
CLASS IV Laser Product
VISIBLE LASER RADIATION-
AVOID EYE OR SKIN EXPOSURE TO
DIRECT OR SCATTERED RADIATION
2w Nd:YAGWavelength: 532 nm
Output Power 20 W
• Exposure to direct beam and scattered
light is eye and skin hazard
• Visible or invisible
• CW power >0.5 W
• Fire hazard
Photo: Keith Hunt - www.keithhunt.co.uk
Copyright: University of Sussex, Brighton (UK)
TYPES OF LASER EYE EXPOSURE
EYE
INTRABEAM
VIEWING
LASER
DIFFUSE
REFLECTION
LASER
SCATTERED
LIGHT
MIRROR
SPECULAR
REFLECTION
LASER
REFLECTED
BEAM
ROUGH
SURFACE
lasersIntro to
CLASS 4 LASER
ND:YAG 1064 nm
100 Watts Max. Average Power
VISIBLE and/ or INVISIBLE LASER
RADIATION-AVOID EYE OR SKIN
EXPOSURE TO DIRECT OR
SCATTERED RADIATION.
Controlled Area Warning Sign
LABORATORY DOOR INTERLOCKlasersIntro to
ENTRYWAY WARNING LIGHTSlasersIntro to
LASER PROTECTIVE BARRIERSlasersIntro to
CURBS ON OPTICAL TABLElasersIntro to
BEAM CONTROLlasersIntro to
COMPUTERS IN RESEARCH LABS
Laser-Professionals.com
Allowing a direct view
from a computer
workstation into a laser
experimental setup
increases the risk of eye
exposure to reflected
beams.
lasersIntro to
LASER SAFETY EYEWEAR
lasersIntro to
EYEWEAR LABELS
All eyewear must be labeled with wavelength and optical density.
lasersIntro to
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