F.Y.B.Sc ( As per SPPU)

1. CHAPTER - 2
LASERS AND LASER APPLICATIONS

2. In 1917:- Einstein Established ‘Stimulated Emission ‘ in black
body radiation.
April 26, 1951:- Charles Hard Townes , Schawlow , Basov ,
Prokhorov of Columbia University in New York
express their ideas about MASER.
MASER:- Microwave Amplification by Stimulated Emission of
Radiation.
May 16, 1960:- Theodore H. Maiman develop first solid
laser Ruby Laser.
December 1960:- Ali Javan, William Bennett Jr. and
Donald Herriott of Bell Labs develop
the gas helium-neon (HeNe) laser
HISTORY

3. LASER :- Light amplification by stimulated emission of
radiation.
Absorption of
Light
Absorption & Emission of Light in Hydrogen Atom
Electronic Configuration of Hydrogen atom : 1S1
Electron Vacant Shells : 2S,2P,3S ……. Etc.

4. Electron in Excited State Electron in Excited State jumps
to Ground State.
Emission of
Light
Emission of Light = E =hϑ

5. THREE PROCESS IN LASER
1) Absorption :-
E1
E2
E1
E2
ρ

6. A + hϑ → A*
Where,
A – Atom in Ground State
A* - Atom in the Excited excited state
Rate of Absorption is,
Rabs = B12 ρ(v)N1
B12 - Einstein Coefficient of induced absorption
ρ(v) – Density of photon
N1- Population of Ground State

7. 2) Spontaneous Emission:-
E1
E2 E2
E1

8. A* → A + hϑ
Where,
A – Atom in Ground State
A* - Atom in the Excited excited state
Rate of spontaneous emission is,
Rsp = A21 N2
A21 - Einstein Coefficient of spontaneous emission
N2- Population of Excited State

9. 3) Stimulated Emission:-
E1 E1
E2
E2

10. A* + hϑ → A
Where,
A – Atom in Ground State
A* - Atom in the Excited excited state
Rate of spontaneous emission is,
Rst = B21 ρ(v)N2
B21 - Einstein Coefficient of stimulated emission
N2- Population of Excited State

11. Difference Between Stimulated Emission &
Spontaneous Emission

12. LIGHT AMPLIFICATION
E1 E1 E1
E2 E2 E2
20
21
22
2n
Intensity of Laser Light = Itotal = N2
I

13. CHARACTERISTICS OF LASER LIGHT
Directionality
In conventional light sources (lamp, sodium lamp and
torchlight), photons will travel in random direction.
Therefore, these light sources emit light in all directions.
In laser, all photons will travel in same direction.
Therefore, laser emits light only in one direction. This is
called directionality of laser light. The width of a laser
beam is extremely narrow.

14. Monochromatic
Monochromatic light means a light containing a single
color or wavelength.
In laser, all the emitted photons have the same energy,
frequency, or wavelength. Hence, the light waves of laser
have single wavelength or color.

15. Coherence
All the photons emitted in laser have the same
energy, frequency, or wavelength, in phase in space
and time.

16. High Intensity
In laser, the light spreads in small region of space and
in a small wavelength range. Hence, laser light has
greater intensity when compared to the ordinary
light.
I = [10/Pλ
]2

17. Beam Divergence
An angular measure of the increase in beam
diameter or radius with distance. For He –Ne
laser 10-3 radian

18. BOLTZMANN DISTRIBUTION LAW
Population:-
The number of atoms per unit volume that occupy a given
energy level.
At temperature ‘T’ ,
Suppose N1 – number of atoms in E1 state
N2 – number of atoms in E2 State
Distribution of atoms in energy levels,
N1 = e-E1/kT
N2 = e-E2/kT
N2/N1 = e-(E2/kT –E1/kT)
N2/N1 = e-(E2 –E1)/kT
N2/N1 = e-ΔE/kT
………………………Boltzmann Distribution law.

19. At thermal equilibrium (T → ∞),
N1 = N2

20. Population Inversion
Number of atoms in excited state is more than
ground state.
N1>> N2 N2>> N1
Non equilibrium
condition
Equilibrium
condition

21. PUMPING
Pumping is process of supplying external energy to laser
medium so that population inversion is achieved.
1) Optical Pumping:- Optical pumping is a process in which
light is used to raise (or "pump") electrons from a lower
energy level in an atom or molecule to a higher one.
Ex.:- Xenon Flash Lamp, Arc Lamp
2) Electrical Discharge :-In this method of pumping, electric
discharge acts as the pump source or energy source.

22. 3)Thermal Pumping
In thermal pumping, heat acts as the pump source or energy
source. The population inversion is achieved by supplying heat
into the laser medium.
4) Chemical Reactions:-
Energy released from chemical reaction is used to pump the
electron from lower energy to higher energy level.
Ex:-Excimer Laser( halogens(F,cl,Br,I) are mixed with inert
gases (xenon, argon)

23. METASTABLE STATE
T = 10-6 TO 10-3 SECOND
E2

24. TWO LEVEL PUMPING SCHEME

25. THREE LEVEL PUMPING SCHEME

26. FOUR LEVEL PUMPING SCHEME

27. TYPES OF LASER
1) Solid Laser
2) Gas Laser
3) Liquid Laser(Dye Laser :-dye rhodamine 6G)
4) Semi Conductor Diode Laser
Most of Lasers emit light in the Red Or
infrared region.

28. COMPONENTS OF LASER
1)Pumping:-
An energy sources such as High voltage Discharge or with
light, Chemical Reactions, Nuclear fission, high-energy electron
beams.
2)Gain Medium or Laser Medium:-
yttrium aluminum garnet(Y3Al5O12),yttrium
orthovanadate (YVO4), or sapphire (Al2O3); and not often cesium
cadmium bromide.
Semiconductors :- e.g. gallium arsenide(GaAs),indium gallium
arsenide (InGaAs), or gallium nitride (GaN),
Gas :- Mixtures of helium and neon (HeNe), nitrogen, argon,
carbon monoxide, carbon dioxide

29. 3) Optical Resonator :-
It is system or set up which is used to obtain the
amplification of stimulated photons by
oscillating them back & forth between system of
two or more mirrors.
One of the mirror is partially reflecting (98%) &
other is fully reflecting(100%).

31. RUBY LASER
Ruby mineral (corundum) is aluminum oxide (Al2O3 ) with
a small amount (about 0.05%) of chromium ions (Cr3+)
which gives it its characteristic pink or red color by
absorbing green and blue light.
Laser Medium : Solid
Active Center: Cr3+
Optical Pumping : Xenon Flash Lamp
Coolant: Liquid nitrogen
Laser Color : Red
Laser Output Form: Pulse
Wavelenth of Laser: 694.3 nm,
Output Power: Output powers up to 36 mW

32. CONSTRUCTION OF RUBY LASER
M1 M2
λ= 5500A0
λ =6943A0

33. 2.26 eV
2.26 eV

34. SPIKES IN RUBY LASER
A laser pulse is not alone, but appears as a train of
pulses in a single envelope. Each pulse train contains
hundreds of close packed pulses, each with a duration
of 1.5-5 [msec]. Each such pulse is called Spike.

35. He –Ne Laser
Laser Medium : Gas
Active Center: Neon
Pumping : Electric Discharge
He:Ne Proportion : 10:1( Helium-90% , Neon 10%)
Laser Color : Red
Wavelength of Laser : 632.8 nm
Laser Output Form: Continuous
Output Power :0.5 to 50 mW.

36. (10:1 proportion)
(100%)
(98%)
CONSTRUCTION OF He –Ne LASER
(5000 V)

37. ENERGY LEVEL DIAGRAM

38. APPLICATIONS OF He- Ne LASER
Laboratories
Barcode scanners
Laser Printer
Non-contact measuring and monitoring:
smoothness of surface
Blood analysis
Particle counting and food sorting

39. APPLICATIONS OF LASER
1)Engineering & Industrial applications :
• Drilling
• Welding
• Vaporization of metals
• Surface hardening
• Cutting metal sheets
• Communication(100s of
messages at time)

40. 2) MEDICAL APPLICATIONS
• Bloodless Surgery
• Ophthalmology
• Excimer Laser: eye surgery
• Brain Surgery: Co2 Laser & Nd-
YAG Laser
• Angioplasty: Argon & Excimer
Laser
• Cancer surgry,removal of
tatoos,mole(unwanted skin
growth :Co2 Laser
• Dentistry:
For painless drilling, welding of
teeth.
• To break kidney stone
40 watt CO2 laser with
applications in gynecology,
dermatology, oral surgery,

41. 3) Scientific Research
• Molecular Structure
• Raman Spectroscopy
• Isotope separation
• Nuclear Fusion Reactor
• Measurement of
earthquakes (laser seismograph)

42. Large Hadron Collider (LHC)
Higgs boson creation in laser-boosted lepton collisions
It’s the physical proof of an invisible, universe-wide field that gave
mass to all matter right after the Big Bang, forcing particles to
coalesce into stars, planets, and everything else.

43. 4)Military
• Directly as an energy weapon
• Guiding a missile or other
projectile or vehicle to a target
by means of a laser beam
• Destroy aeroplanes,missile,
tanks
• Thermal Imaging
• Night vision

44. Holography
Dennis Gabor who was awarded the prize 1971 for his
‘invention and development of the holographic method’.

45. LIDAR
It is a method for measuring distances by illuminating
the target with laser light and measuring the reflection
with a sensor. Differences in laser return times and
wavelengths can then be used to make digital 3D
representations of the target.
Applications of LIDAR:-
High-resolution maps, Surveying, Archaeology, Geography,
Geology, Geomorphology, Forestry, Atmospheric Physics