Introduction of Laser

1. LASER

2. Definition
 The acronym LASER stands for Light
Amplification by Stimulated Emission of
Radiation
 A laser is a device that generates light by
a process called STIMULATED
EMISSION.
 Laser light is a coherent beam

3. Background Physics
 In 1916 Einstein predicted that:
 Under certain circumstances a photon
incident upon a material can generate a
second photon of
o Exactly the same energy (Frequency)
o Phase
o Polarization
o Direction of propagation
 In other words, a coherent beam resulted.

4. Properties of laser
 Directionality
 Negligible divergence
 High intensity
 Coherence
 Monochromatic

5. Mechanisms of Light Emission
1. Absorption
2. Spontaneous Emission
3. Stimulated Emission
Therefore 3 process
of light emission:
E1
E2
h
(a) Absorption
h
(b) Spontaneous emission
h
(c) Stimulated emission
In
h
Out
h
E2 E2
E1 E1
Absorption, spontaneous (random photon) emission and stimulated
emission.
© 1999 S.O. Kasap,Optoelectronics (Prentice Hall)

6. Absorption
Probability of absorption
12
12 12
P ( )
P ( )
v
B v




B12 – Einstein coefficient
for absorption
E1
E2

7. Spontaneous Emission
Probability of Spontaneous Emission
21(Spont) 21P A A21 – Einstein coefficient
for Spontaneous
Emission
E1
E2

8. Stimulated Emission
Probability of Stimulated Emission
21(Stimu)
21(Stimu) 21
P ( )
P ( )
v
B v




B21 – Einstein coefficient
for Stimulated
Emission
E1
E2

9. Population Inversion
 For lasing action N2 > N1
 Population inversion can be created by
introducing a so call meta-stable centre
where electrons can piled up to achieve a
situation where more N2 than N1
 The process of attaining a population
inversion is called pumping and the
objective is to obtain a non-thermal
equilibrium

10. Types of Laser
 Based on the mechanism in which
Population Inversion is achieved
(i) Three level lasers
(ii) Four level lasers
 Based on state of active medium used
(i) Gas Laser
(ii) Solid state Laser
(iii) Semiconductor Laser
(iv) Tunable dye Laser

11. Nd:YAG Laser
 Nd:YAG - Neodymium doped yttrium
aluminium garnet
4 level laser systems
YAG is hosts in which Neodymium ions is
active center
 Properties
For continuous or very high pulse rate
Emission wavelength - 1.06 µm

12. Nd:YAG LASER Energy Level

13. Nd:YAG LASER Syematic

14. Applications
Cutting
Welding
Scribing
Soldering
Trimming
Fibre Optics Communication

15. Thanks. . . . . .