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Lasers
Introduction to

2. Lecture Contents
•
•
•
•
•
•
Laser Applications
Definition of lasers
Population Inversion
Materials used for semiconducting laser
Quantum dot devices
Laser Safety
Intro to
lasers

3. Intro to
lasers
Laser Applications
TELECOMMUNICATION
10 Gbits /s
FLAG network
From UK to Japan
(Fiber-optic Link Around the Globe)
28OOOKM
Flag Network owned by
Reliance Globecom -UK
Flag Network Collaboration In India
Reliance Communications

4. Another Typical Application of
Laser – Fibre Optics
• 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.
Intro to
lasers

5. Laser Applications
MEDICINAL PURPOSE
#
Intro to
lasers
Fiber optic
Endoscopeto
Detect ulcers
in the intestines.
Lasers are used extensively
in the treatment of
eye-diseases ,particularly to
reattach a detached retina.
Bloodless Surgery.
# The liver and lung diseases could be
treated using lasers.

6. Laser Applications
MEDICINAL PURPOSE
Intro to
lasers
• To destroy cancerous and precancerous cells; at the same
time, the heat seal off capillaries,
To break up gallstones and
kidney stones
To remove plaque clogging
human arteries

7. Laser Applications
INDUSTRIAL PURPOSES
Intro to
lasers
#
lasers are used now for cutting, drilling and
welding of metals and other materials.
Laser light is used to collect the
information about the prefixed prices of
various products in shops and
business establishments from the barcode printed on the product.
• LIDAR –Light Detection & Ranging (Mines)
• Leveling of Ceramic Tile Floor
# For precision measurements & leveling

8. Laser Applications
INDUSTRIAL PURPOSES
PC-board CAD tools s
3D printers
Latching tool
Intro to
lasers
Milling 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.

9. Laser Applications
DEFENCE & SECURITY
Intro to
lasers
#
LASTEC- HPL Researches
(Laser Science & Technology Centre) # In sniper guns, for target acquisition & locking
Dragunov SVD – Semi Automatic Sniper gun
Under DRDO
(Defence Research & Development Organisation)
Indian ARM industry :- OFB (Ordinance Factories Board )

10. MILITARY USES
THERMAL IMAGING
THERMAL IMAGING
• Laser guided munitions
– Designated from air or ground
Intro to
lasers
• Thermal homing missiles
• Optical Guidance
• Night Vision

11. 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)
@ www.gizmag.com/millitarygadgets
Intro to
lasers

12. Intro to
lasers
Laser Applications
HOLOGRAPHY
• Holography is the production of holograms by the use of laser.
@ www.pranavmistry.com

13. Laser Applications
HOLOGRAPHY
• Possible medical applications using the technology
– Surgical procedures (using tracking capabilities)
– Rehabilitation techniques & Gaming
Intro to
lasers

14. 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!
Intro to
lasers

15. BASIC LASER
Light
Amplification by
Stimulated
Emission of
Radiation
Intro to
lasers

16. Definition of
laser
• A laser is a device that generates light by a process
called STIMULATED EMISSION.
• The acronym LASER stands for Light Amplification
by Stimulated Emission of Radiation
• Semiconducting lasers are multilayer semiconductor
devices that generates a coherent beam of
monochromatic light by laser action. A coherent
beam resulted which all of the photons are in
phase.
Intro to
lasers

17. Electromagnetic Spectrum
Gamma Rays
10-13
10-12
10-11
X-Rays
10-10
10-9
Ultra- Visible
violet
Infrared
10-8
10-5
10-7
10-6
Microwaves
10-4
10-3
10-2
Radar
waves
10-1
TV
waves
1
10
Radio
waves
102
Wavelength (m)
LASERS
Retinal Hazard Region
Ultraviolet
200
300
Visible
400
500
600
Near Infrared
700
800
900
1000
1100
Far Infrared
1200
1300
1400
1500
10600
Wavelength (nm)
ArF
193
XeCl
308
KrF
248
Ar
488/515
HeNe Ruby
633 694
2w
Alexandrite GaAs
Nd:YAG
755
905
532
Nd:YAG
1064
Communication CO2
10600
Diode
1550
Lasers operate in the ultraviolet, visible, and infrared.
Intro to
lasers

18. Properties of Laser Light
• 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
Intro to
lasers

19. Types of LASERS
LASERS
Semiconductor
Diode Laser
Solid state
Liquid
Gas Lasers
Solid state
Liquid
Neodymium Yag Laser
Ruby laser
Gaseous
Intro to
lasers

20. Market demand of QD lasers
( QUANTUM DOT )
Microwave/Millimeter wave
transmission with optical fibers
Datacom
network
Telecom
network
QD Lasers
High speed QDL
Directly Modulated Quantum
Dot Lasers
•Datacom
Mode-Locked Quantum Dot
Lasers
Optics
Advantages
•Short
InP Based Quantum Dot
Lasers
•Low
@ www.fibers.org
Intro to
lasers
application
•Rate of 10Gb/s
optical pulses
•Narrow spectral width
•Broad gain spectrum
•Very low α factor-low chirp
emission wavelength
•Wide temperature range
•Used for data transmission

21. DEFINITION OF MPE
The level of laser light to which a person may be
exposed without risk of injury.
Intro to
lasers

22. Mechanisms of Light Emission
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:
1. Absorption
2. Spontaneous Emission
3. Stimulated Emission

23. 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.”
Intro to
This process is called stimulated emission.
lasers

24. Intro to
lasers
Stimulated Emission
Emitted
photon
Incident
photon
Excited
electron
Incident
photon
Unexcited
electron
Before emission
After emission

25. Intro to
lasers
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
Excited system
E3
E2
E3
E2
E1
E1

26. Metastable State
Intro to
lasers
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.
E3
Metastable state
E3
E2
E2
Incident photon
Photon of energy E 2  E1
E1
Metastable system
E1
Emitted photon
Stimulated emission

27. Common Laser System
Intro to
lasers

28. Intro to
lasers
BASIC LASER COMPONENTS
ACTIVE MEDIUM
Optical Resonator
Solid (Crystal)
Gas
Semiconductor (Diode)
Liquid (Dye)
EXCITATION
MECHANISM
Optical
Electrical
Chemical
OPTICAL
RESONATOR
HR Mirror and
Output Coupler
Active
Medium
High Reflectance
Mirror (HR)
Output
Beam
Output Coupler
Mirror (OC)
Excitation
Mechanism
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.

29. Laser Wavelength Linewidth
Intro to
lasers

30. CDRH CLASS WARNING LABELS
Laser Radiation
Do Not Stare Into Beam
Helium Neon Laser
1 milliwatt max/cw
CLASS II LASER PRODUCT
Class II
Class IIIa with expanded beam
VISIBLE LASER RADIATIONAVOID EYE OR SKIN EXPOSURE TO
DIRECT OR SCATTERED RADIATION
Argon Ion
Wavelength: 488/514 nm
Output Power 5 W
CLASS IV Laser Product
Class IIIa with small beam
Class IIIb
Class IV
Intro to
lasers

31. INTERNATIONAL LASER WARNING LABELS
INVISIBLE LASER RADIATION
AVOID EYE OR SKIN EXPOSURE
TO DIRECT OR SCATTERED RADIATION
CLASS 4 LASER PRODUCT
WAVELENGTH
MAX LASER POWER
EN60825-1
Symbol and Border: Black
Background: Yellow
10,600 nm
200 W
1998
Legend and Border: Black
Background: Yellow
Intro to
lasers

32. Intro to
NEODYMIUM YAG LASER
lasers
Courtesy of Los Alamos National Laboratory
Rear Mirror
Adjustment Knobs
Safety Shutter Polarizer Assembly (optional)
Coolant
Beam
Tube
Adjustment
Knob
Output
Mirror
Beam
Q-switch
(optional)
Beam Tube
Nd:YAG
Laser Rod
Flashlamps
Pump
Cavity
Laser Cavity
Harmonic
Generator (optional)
Medium :- Neodymium-Doped Yttrium Aluminum Garnet Crystal
State :- Solid
Excitation :- Diode Laser
Beam :- 1064 nm infrared
Uses :- Cataract ,Glaucoma , Gingivectomy surgeries

33. Intro to
lasers
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
hc
 Eg

hc
1.24
 m )


E g E g eV )

34. LASER HAZARD CLASSES
Lasers are classified according to the level of laser radiation that
is accessible during normal operation.
Intro to
lasers

35. CLASS 1
• Safe during normal use
• Incapable of causing injury
• Low power or enclosed beam
CLASS I Laser Product
Label not required
Nd:YAG Laser Marker
May be higher class during
maintenance or service

36. CLASS 2
•
•
•
•
Staring into beam is eye hazard
Eye protected by aversion response
Visible lasers only
CW maximum power 1 mW
Laser Scanners
Laser Radiation
Do Not Stare Into Beam
Helium Neon Laser
1 milliwatt max/cw
CLASS II LASER PRODUCT

37. CLASS 3R (Formerly 3a)
• Aversion response may not provide
adequate eye protection
• CDRH includes visible lasers only
• ANSI includes invisible lasers
• CW maximum power (visible) 5 mW
Expanded Beam
Laser Pointers
Laser RadiationDo Not Stare Into Beam or View
Directly With Optical Instruments
Helium Neon Laser
5 milliwatt max/cw
CLASS IIIa LASER PRODUCT
LASER RADIATIONAVOID DIRECT EYE EXPOSURE
ND:YAG 532nm
5 milliwatts max/CW
CLASS IIIa Laser Product
Small Beam

38. CLASS 3B
DPSS Laser with cover removed
• Direct exposure to beam is eye hazard
• Visible or invisible
• CW maximum power 500 mW
LASER RADIATIONAVOID DIRECT EXPOSURE TO BEAM
2w ND:YAG Wavelength: 532 nm
Output Power 80 mW
CLASS IIIb Laser Product
Courtesy of Sam’s Laser FAQ, www.repairfaq.org/sam/lasersam.htm, © 1994-2004

39. CLASS 4
• Exposure to direct beam and scattered
light is eye and skin hazard
• Visible or invisible
• CW power >0.5 W
• Fire hazard
VISIBLE LASER RADIATIONAVOID EYE OR SKIN EXPOSURE TO
DIRECT OR SCATTERED RADIATION
Photo: Keith Hunt - www.keithhunt.co.uk
Copyright: University of Sussex, Brighton (UK)
2w Nd:YAG
Wavelength: 532 nm
Output Power 20 W
CLASS IV Laser Product

40. TYPES OF LASER EYE EXPOSURE
INTRABEAM
VIEWING
EYE
LASER
SPECULAR
REFLECTION
LASER
DIFFUSE
REFLECTION
LASER
REFLECTED
BEAM
MIRROR
SCATTERED
LIGHT
ROUGH
SURFACE
Intro to
lasers

41. VISIBLE and/ or INVISIBLE LASER
RADIATION-AVOID EYE OR SKIN
EXPOSURE TO DIRECT OR
SCATTERED RADIATION.
ND:YAG 1064 nm
100 Watts Max. Average Power
CLASS 4 LASER
Controlled Area Warning Sign

42. Intro to
lasers
LABORATORY DOOR INTERLOCK

43. Intro to
lasers
ENTRYWAY WARNING LIGHTS

44. Intro to
lasers
LASER PROTECTIVE BARRIERS

45. Intro to
lasers
CURBS ON OPTICAL TABLE

46. Intro to
lasers
BEAM CONTROL

47. Intro to
lasers
COMPUTERS IN RESEARCH LABS
Allowing a direct view
from a computer
workstation into a laser
experimental setup
increases the risk of eye
exposure to reflected
beams.
Laser-Professionals.com

48. LASER SAFETY EYEWEAR
Intro to
lasers

49. EYEWEAR LABELS
Intro to
lasers
All eyewear must be labeled with wavelength and optical density.

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