The document discusses lasers, including their history, characteristics, components, types, and applications. It begins with defining what a laser is, describing early developments in stimulated emission. Key points made include: - Lasers emit highly directional, intense beams of coherent, monochromatic light. - The first working laser was a ruby laser developed by Maiman in 1960. - Laser light has properties of directionality, coherence, monochromaticity, and high intensity compared to other light sources. - The main components of a laser system are the power source, active medium which is pumped to induce stimulated emission, and optical cavity. - Common laser types include solid state, gas, liquid,

3. Introduction of laser
 The word laser is an acronym that stands for
“Light Amplification by Stimulated Emission of Radiation”.
 Lasers are essentially highly directional, highly intense, highly
monochromatic and highly coherent optical sources.
 Stimulated emission was postulated by Einstein as early as in
1917.
 In 1960 , a solid state ruby laser is developed by T. H. Maiman on
this principle.
 In 1961, a gas state He-Ne laser was developed by Ali Javan and
others in Bell telephone laboratory.

4. Incandescent lamp Vs LASER
Ordinary Light LASER
It is not coherent It is highly coherent
It is not directional It is more directional
It is not monochromatic It is monochromatic
It is less intense It is highly intense
Angular spread is more Angular spread is very less
The radiations are polychromatic The radiations are monochromatic
Examples: Sunlight, Mercury vapour
lamp
Examples: He-Ne Laser, Ruby Laser,
CO2 laser, etc.

5. Characteristics Of Laser Light
 Highly Directionality
 High Monochromatic
 High Coherence
 High Intense

6. 1.Directionality
During the propagation of a LASER beam, its angular speed is very less and the beam
occupies the less area. Hence, it travels along only a particular direction through longer
distances.
The Laser light of wavelength 𝜆 emerges through laser source aperture diameter
“d” then it propagates as parallel beam up to d2
∕ 𝜆 (small values) and gets diverged. The angle
of divergence of a laser beam is expressed as
𝜙=
𝑎𝑟𝑐
𝑟𝑎𝑑𝑖 𝑢𝑠
=
𝑑2−𝑑1
𝑠2−𝑠1
where d1 and d2 are the diameters of the laser spots measured at distances s1 and s2from the
LASER aperture. For LASER light ∅ = 10-3
radians
It clear from the above value, that the divergence is low and it is highly directional

7. 2. Monochromaticity: The property of exhibiting single wave length is called
Monochromaticity a Laser beam will have single wavelength and it is
monochromatic.
Ex: Ruby Laser = 6943A0
Semiconductor Laser = 8000A0
Explanation:- In Laser radiation all the photons emitted between discrete
energy levels will have same wave length As result the radiation is
monochromatic in nature, If the higher energy level has closely spaced
energy levels then from the transition from each level to lower energy level
emits photons of different frequencies and wavelengths
Let the spread in frequency and wavelength be 𝜈 + ∇𝜈 and 𝜆+Δ𝜆 the
frequency spread
∇𝜈 is related to its wavelength spread Δ𝜆 as
Δ𝜆 =- (c/𝜈2
) ∇𝜈
For Laser Δ𝜆=0.001nm It clear that laser radiation is highly monochromatic

8. 3. Brightness: Due to its directionality the intensity of Laser beam is very more.
Hence its brightness is high. Hence laser is used for welding and cutting purposes.
4.Coherence: When two or more waves have same frequency and have same
phase (or) Zero phase difference, then those waves are called coherent waves. In a
Laser beam all the Laser waves exactly have same phase.
Coherence is of two types.
(a) Temporal Coherence
(b) Spatial Coherence:

9. Principle for LASER Action:
The interaction of light with matter is responsible for Laser action. When light travels
through the medium then three different processes are occurred. They are
1. Stimulated Absorption or Absorption
2. Spontaneous Emission of Radiation
3. Stimulated Emission of Radiation

10. 1. Stimulated Absorption or Absorption
The number of stimulated absorptions depend upon the number of atoms per unit volume N1
in E1 and the number of photons per unit volume of incident radiation i.e. Incident radiation
density u(𝜗) i.e.
Number of stimulated absorption ∝ N1
∝ u (𝜗)
∝ N1 u (𝜗)
= N1B12 u (𝜗)
Where B12 is Known as Einstein’s coefficient of stimulated absorption of radiation
E1
E2
N1
N2

11. 2. Spontaneous Emission of Radiation
The process of transits atoms from higher level to the lower energy level by itself after
the completion of 10-8s.
Ex: Radiation emitted by glowing electric bulb and glowing candle.
The energy difference is given by E= E2- E1
h = E2- E1
 = E2 - E1 /h
The number of Spontaneous emission of radiation depends on the number of atoms per unit volume
in E2, i.e. N2
Number of Spontaneous emissions N2
= N2A21
Where A21 is known as Einstein’s coefficient of Spontaneous emission of radiation
A*- h +A

12. 3. Stimulated Emission of Radiation
The emission process in which an atom in excited level is brought down to the ground
level by an external force before the completion of 10 – 8
s is called stimulated emission.
This transition emits a photon of energy E= E2- E1
𝜗 = E2- E1 /h
The number of stimulated emissions depends on the number of atoms in the higher
energy level E1 , i.e.,N2 and the incident radiation density u (𝜗)
Number of stimulated absorption ∝ N2
∝ u (𝜗)
∝ N2 u (𝜗)
= N2B21 u (𝜗)
Where B21 is Known as Einstein’s coefficient of stimulated emission of radiation
Ex: Emission of laser beam

13. Spontaneous emission Stimulated emission
1. Emission of a photon by an atom without any
external force is called “Spontaneous
emission”.
2. Light emitted through this process is
incoherent.
3. The net intensity proportional to the no of
radiating atoms.
4. Light resulting through this process is not
monochromatic
5. Less directionality
6. Light from sodium lamp (or) mercury lamp
7. Proposed by Bohr.
1. The emission of two photons by an atom
when it is present at excited state due to
action of external force in called “Stimulated
emission”.
2. Light emitted through this process is
coherent
3. The net intensity of light is proportional to
the square of no. of atoms radiating light.
4. Light resulting through this process in
chromatic.
5. High directionality
6. Light from a Laser source.
7. Proposed by Einstein.
Differences Between Spontaneous and Stimulated Emission

14. Population Inversion:
The stage of making the number of atoms more in the high energy level than the lower
energy level is called as population inversion.
N1 > N2 > N3
N1
N2
N3
N2>N1
The process of sending atoms from E1 to E2 to get population inversion is known as pumping

15. Pumping mechanisms
Optical Pumping
Electric discharge
Pumping
Inelastic Atom-Atom
Collision
Chemical Reaction
Ruby LASER HF LASERHe-Ne LASERArgon Ion LASER

16. Construction and Components of Laser system
Laser system has three important components. They are
1. Source of energy
2. Active medium
3. Optical Cavity or Resonator

17. Types of LASERs
Among the various kinds of lasers some important types of lasers are listed below:
1. Solid State Laser (Ex. Ruby Laser, Nd: YAG Laser)
2. Gas Laser (Ex. He-Ne Laser, CO2 Laser)
3. Liquid Laser (Ex. Europium Chelate Laser)
4. Dye Laser (Ex. Methyle Alcohol, Rhodamine 6G Laser)
5. Semiconductor Laser (Ex. GaAs, InP Laser)

18. Typical Lasers And Their Emission Wavelengths
LASERs Wavelengths (nm)

19. Construction and working principle of He-Ne laser
Construction:
 A He-Ne laser consists of large and narrow discharge tube filled with helium a and neon gases in the ratio
10:1.
 The tube is enclosed between fully and partially reflective mirrors which serve as optical cavity.
 The two end windows are set at Brewster's angle, so reflected radiations enter into the tube become
polarized.
Gas laser was invented in 1961 by Ali Javane. It is four level laser system, it is useful in making holograms etc.
Source of energy : RF oscillator
Active medium : He + Ne gas mixture
Optical Cavity : Quartz tube

20. Working Principle of He-Ne Laser

21. Applications of Lasers in various fields
 Medical Applications
 Industrial Applications
 Communication Applications
 Military Applications
 Scientific Research
 Chemical Applications

23. Medical Applications
Laser Eye Surgery

24. Laser in MRI
( Magnetic
Resonance
Imaging )
Laser In
Eye
Treatment

26. Laser Tattoo Removal

27. LASERs in Industry

31. Laser in Heat Treatment

32. Laser in Garment Industry

34. CO2 laser engraving Designs
Laser Textile Stitching

35. Laser In Surveying And Ranging

36. Lasers In Communication

39. Laser In Barcode
Scanning

41. Laser in Data Storage

45. Laser In
Holography

46. Scientific Research
Laser In Spectroscopy

48. LASERs in Military

57. Chemical Applications

58. Biological cells shape and size

59. Isotopes separation