for all

1. LASER

2. What is Laser?
Light Amplification by Stimulated
Emission of Radiation
• A device produces a coherent beam of optical
radiation by stimulating electronic, ionic, or
molecular transitions to higher energy levels
• When they return to lower energy levels by
stimulated emission, they emit energy.

3. Properties of Laser
• Monochromatic
• Coherent
• Directional

4.  The light emitted from a laser is monochromatic, that is, it is of one
color/wavelength. In contrast, ordinary white light is a combination of
many colors (or wavelengths) of light.
 Lasers emit light that is highly directional, that is, laser light is emitted as
a relatively narrow beam in a specific direction. Ordinary light, such as
from a light bulb, is emitted in many directions away from the source.
 The light from a laser is said to be coherent, which means that the
wavelengths of the laser light are in phase in space and time. Ordinary
light can be a mixture of many wavelengths.
 These three properties of laser light are what can make it more
hazardous than ordinary light. Laser light can deposit a lot of energy
within a small area.

5. Basic concepts for a laser
• Absorption
• Spontaneous Emission
• Stimulated Emission
• Population inversion

6. Absorption
• Energy is absorbed by an atom, the electrons are
excited into vacant energy shells.

7. Spontaneous Emission
• The atom decays from level 2 to level 1 through the
emission of a photon with the energy hv. It is a
completely random process.

8. Stimulated Emission
atoms in an upper energy level can be triggered or
stimulated in phase by an incoming photon of a specific
energy.

9. Stimulated Emission
The stimulated photons have unique properties:
– In phase with the incident photon
– Same wavelength as the incident photon
– Travel in same direction as incident photon

10. Population Inversion
• A state in which a substance has been energized, or
excited to specific energy levels.
• More atoms or molecules are in a higher excited
state.
• The process of producing a population inversion is
called pumping.
• Examples:
→by lamps of appropriate intensity
→by electrical discharge

11. Lasing Action
1. Energy is applied to a medium raising electrons to an unstable energy
level.
2. These atoms spontaneously decay to a relatively long-lived, lower
energy, metastable state.
3. A population inversion is achieved when the majority of atoms have
reached this metastable state.
4. Lasing action occurs when an electron spontaneously returns to its
ground state and produces a photon.
5. If the energy from this photon is of the precise wavelength, it will
stimulate the production of another photon of the same wavelength
and resulting in a cascading effect.
6. The highly reflective mirror and partially reflective mirror continue the
reaction by directing photons back through the medium along the long
axis of the laser.
7. The partially reflective mirror allows the transmission of a small amount
of coherent radiation that we observe as the “beam”.
8. Laser radiation will continue as long as energy is applied to the lasing
medium.

12. Two-level Laser System
• Unimaginable
as absorption and stimulated processes
neutralize one another.

13. 14
Lasing Action Diagram
Energy
Introductio
Ground State
Excited State
Metastable State
Spontaneous
Energy Emission
Stimulated Emission
of Radiation

14. How a laser works?

15. 1. High-voltage electricity causes the
quartz flash tube to emit an intense
burst of light, exciting some of Cr3+
in the ruby crystal to higher energy
levels.
2. At a specific energy level, some
Cr3+
emit photons. At first the photons
are emitted in all directions. Photons
from one Cr3+
stimulate emission
of photons from other Cr3+
and the
light intensity is rapidly amplified.

16. 3. Mirrors at each end reflect the
photons back and forth, continuing
this process of stimulated emission
and amplification.
4. The photons leave through the
partially silvered mirror at one
end. This is laser light.

17. Three-level Laser System
• Initially excited to a
short-lived high-
energy state .
• Then quickly decay to
the intermediate
metastable level.
• Population inversion is
created between
lower ground state
and a higher-energy
metastable state.

18. Three-level Laser System
mµλ 6943.0=
s7
3
10τ −
≈ s3
2
103τ −
⋅≈
Ruby laser
23 ττ <<

19. Four-level Laser System
• Laser transition takes
place between the third
and second excited
states.
• Rapid depopulation of
the lower laser level.

20. 1.06 mλ µ=
4
2τ 2.3 10 s−
≈ ×
2 0.6328 mλ µ=
100nsτ2
≈ 10nsτ1
≈
Four-level Laser System
Nd:YAG laser
He-Ne laser
23 ττ <<

21. Laser Construction
• A pump source
• A gain medium or laser medium.
• Mirrors forming an optical resonator.

22. Laser Construction

23. Pump Source
• Provides energy to the laser system
• Examples: electrical discharges, flashlamps, arc
lamps and chemical reactions.
• The type of pump source used depends on the
gain medium.
→A helium-neon (HeNe) laser uses an
electrical discharge in the helium-neon gas
mixture.
→Excimer lasers use a chemical reaction.

24. Gain Medium
• Major determining factor of the wavelength of
operation of the laser.
• Excited by the pump source to produce a
population inversion.
• Where spontaneous and stimulated emission of
photons takes place.
• Example:
solid, liquid, gas and semiconductor.

25. Optical Resonator
• Two parallel mirrors placed around the gain
medium.
• Light is reflected by the mirrors back into the
medium and is amplified .
• The design and alignment of the mirrors with
respect to the medium is crucial.
• Spinning mirrors, modulators, filters and
absorbers may be added to produce a variety
of effects on the laser output.

26. Laser Types
• According to the active material:
solid-state, liquid, gas, excimer or
semiconductor lasers.
• According to the wavelength:
infra-red, visible, ultra-violet (UV) or x-ray
lasers.

27. 28
Argon fluoride (Excimer-UV)
Krypton chloride (Excimer-UV)
Krypton fluoride (Excimer-UV)
Xenon chloride (Excimer-UV)
Xenon fluoride (Excimer-UV)
Helium cadmium (UV)
Nitrogen (UV)
Helium cadmium (violet)
Krypton (blue)
Argon (blue)
Copper vapor (green)
Argon (green)
Krypton (green)
Frequency doubled
Nd YAG (green)
Helium neon (green)
Krypton (yellow)
Copper vapor (yellow)
0.193
0.222
0.248
0.308
0.351
0.325
0.337
0.441
0.476
0.488
0.510
0.514
0.528
0.532
0.543
0.568
0.570
Helium neon (yellow)
Helium neon (orange)
Gold vapor (red)
Helium neon (red)
Krypton (red)
Rohodamine 6G dye (tunable)
Ruby (CrAlO3
) (red)
Gallium arsenide (diode-NIR)
Nd:YAG (NIR)
Helium neon (NIR)
Erbium (NIR)
Helium neon (NIR)
Hydrogen fluoride (NIR)
Carbon dioxide (FIR)
Carbon dioxide (FIR)
0.594
0.610
0.627
0.633
0.647
0.570-0.650
0.694
0.840
1.064
1.15
1.504
3.39
2.70
9.6
10.6
Key: UV = ultraviolet (0.200-0.400 µm)
VIS = visible (0.400-0.700 µm)
NIR = near infrared (0.700-1.400 µm)
WAVELENGTHS OF MOST COMMON LASERS
Wavelength (µm)Laser Type

28. Solid-state Laser
• Example: Ruby Laser
• Operation wavelength: 694.3 nm (IR)
• 3 level system: absorbs green/blue
•Gain Medium: crystal of aluminum oxide (Al2O3)
with small part of atoms of aluminum is replaced
with Cr3+
ions.
•Pump source: flash lamp
•The ends of ruby rod serve as laser mirrors.

29. Liquid Laser
• Example: dye laser
• Gain medium: complex organic dyes, such as
rhodamine 6G, in liquid solution or
suspension.
• Pump source: other lasers or flashlamp.
• Can be used for a wide range of wavelengths
as the tuning range of the laser depends on
the exact dye used.
• Suitable for tunable lasers.

30. Schematic diagram of a dye laser
dye laser
A dye laser can be considered to be basically a four-level system.
The energy absorbed by the dye creates a population inversion, moving the
electrons into an excited state.

31. Gas Laser
• Example: Helium-neon laser (He-Ne laser)
• Operation wavelength: 632.8 nm
• Pump source: electrical discharge
• Gain medium : ratio 5:1 mixture of helium and
neon gases

32. Excimer Laser
• cool laser.
• Incredibly precise.
• laser eye surgery.
Excimer laser used for eye surgery.

33. Semiconductor laser
Semiconductor laser is a laser in which semiconductor serves as photon
source.

34. Applications of laser
• Industry & Commercial
a. cutting, welding, marking
b. CD player, DVD player
c. Laser printers, laser pointers
d. Photolithography
e. Laser light display

35. Applications of laser
• Medical
a. eye surgery
b. cosmetic surgery

36. Applications of laser
• Scientific
a. Spectroscopy
b. Lunar laser ranging
c. Photochemistry
d. Nuclear fusion

37. Military Applications of Laser

38. Applications
Non-Weapon Compact systems
EOCM Lasers HPL-DEW
Directed Energy Systems
Battlefield Lasers
Compact, low
power Lasers.
- LRF / Target
Designator
- Underwater
Ranging
- Laser Bathymetry
- Laser Trackers
- Ring Laser Gyro
- Laser Proximity
fuse
- Submarine Laser
Communication
Moderate Power Laser for
Anti sensor /Anti-Personnel
use.
- Soft kill – Low Intensity
Warfare
- Disabling of EO sensors
IR camera, CCD etc
- Damage to front-end
optics
- Dazzling of Military
Operators
- Range – upto 20 km
- EOCM class Laser types :
Pulsed solid state lasers like
Nd:YAG/Glass, Alexandrite
High power Lasers.
- Burning holes in critical
structure like fuel tank of
aircrafts,H’copters, Missiles
- Damage to vulnerable
points like: Sensors, Optics
of Helicopters, Aircrafts &
Missiles
- Range 5-20 km
- Laser types :
Chemical, Dynamic Gas
lasers -
CO2 , HF/DF, COIL, FEL

39. LASER RANGE FINDER
•Laser range finders (LRFs) are vital components of high
precision targeting engagements.
•The precise and accurate range-to-target information is an
essential variable in the fire control solution of today’s
sophisticated weapons.
•During the Persian Gulf War (Aug 90 to Feb 91), the effective
use of Laser based devices were amply demonstrated.
•LRFs (along with laser target designators and laser-guided
smart bombs) were perhaps the most used and reliable devices
that used Laser technology.

40. LASER RANGE FINDER
Requirement : For Acquiring and Locating a target before any
tactical decision is taken in the battlefield scenario.
Works on the principle of a RADAR. A collimated pulse is
directed towards a target and the reflected light is received and
detected.
Range = C×t/2
where t is the round trip time

41. LASER TARGET ILLUMINATOR
•This is a device which illuminates a target/group of targets or
area with laser radiation.
• The use of laser illuminators are varied, including use as a
non-lethal weapon or as a source of laser energy for laser
guided weapons to home in on.
Suitable Lasers:
1. Nd: YAG laser
2. Diode Pumped Solid State laser
3. Semiconductor laser

42. LASER DAZZLER
• The Laser Illuminator
temporarily impairs an
adversary’s ability to fire a
weapon or to otherwise
threaten friendly forces.
• The laser briefly illuminates
an opponent with harmless,
low-power laser light from a
Semiconductor laser or a
Solid State laser.

43. A weapon which uses a seeker to
detect laser energy reflected from a target
marked by a laser, and through signal
processing provides guidance commands to
a control system which guides the weapon to
the point from which the laser energy is
being reflected
LASER GUIDED WEAPON (LGW)

45. LGWs
A laser-guided GBU-24
strikes its target

46. •Higher Accuracy
•Less Munitions Required
•Less Civilian Casualties
•Greater Target Damage
•Simple to Convert From Old Munitions
WHY LGWs

47. High Energy Laser
Weapons

48. Laser DEW

49. Lethal Laser Weapons
Pump Power
Laser Medium
LASER
LASER
A Directed Energy Lethal Weapon (DEW) exploits the High Power
Laser Radiation for causing the intended Damage to the Target.
Destroys Targets by
Melting & Weakening
the Structures,
Igniting the Explosive
Fillers etc.
Beam Director for
Remote Focusing
Speed of Light Delivery of
Speed of Light Delivery of
Lethal Energy
Lethal Energy
Converts Chemical / Electrical
Energy into Light Energy

50. Capabilities – High Power Laser DEWs
• Engagement at the speed of light
Reduces challenges of late detection and maneuvering threats
• Precision application of energy
Small engagement spot size on threat target lowers risk of collateral damage
• High resolution target imaging and target tracking
High kill probability – beam on target until kill is confirmed
• Low cost per kill
Only fuel is consumed, no hardware is launched
• Stealth - invisible beam
• Deep magazine with rapid recharging
Limitations
• Line-of-Sight Dependence
• Weather conditions
• Minimal Effects on
Hardened Structures and
Armored Vehicles

51. International Status
Avenger Laser System, USA
ZEUS USA
Thor - Israel
 Remote Neutralization of
Unexploded Ordnance,
Surface Landmines and
Improvised Explosive
Devices (IED’s)
 Effective Standoff Operational
Range – (200-250) meters

52. UAVs / DRONES
Structure Material
-Aluminum / Steel
-Wood
-Carbon Fiber
Composites
-Glass Fiber Reinforced
Plastics
Damage Mechanism
-Heating (structure weakening)
-Combustion (Burning)

53. ABL to Destroy Ballistic Missiles
US defence along with DARPA is developing a 20MW DF laser for destroying the
ICBM

54. Interesting Facts..
•Laser Target Designators were used during the Persian Gulf
War to direct Precision Guided Munitions such as the
GBU – 12 and the Hellfire laser guided bombs.
•Stealth F-117 aircraft was also laser assisted for attacks
against Baghdad.
•Apache helicopters armed with hellfire destroyed 2 radar
sites in Western Iraq.
•Out of the 20,000 PGMs used in the Persian Gulf War, more
than 60% were laser guided.
•Laser Guided bunker buster bombs destroyed the hide-outs
of Osama in Tora Bora in Afghanistan.