This document defines lasers and describes their applications. It begins by explaining that a laser generates light through stimulated emission of radiation. Lasers produce coherent, monochromatic beams of light. Semiconductor lasers are used in applications like compact discs, where a laser is focused onto the disc to detect binary data stored as pits. Diode lasers are another example of a semiconductor laser. Fibre optics use lasers as a light source because lasers produce coherent beams that can carry information over long distances with little signal loss. The document also discusses the three mechanisms of light emission: absorption, spontaneous emission, and stimulated emission, with stimulated emission being the key process that produces the coherent light in lasers.

1. Prepared by:-
Kajal barad(151080106002)
Guided by:-
Medha shah
LASER

2. 1. 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.

3. 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!

4. Diode Laser

5. 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.

6. Fibre Optics Communication

7. 3 Mechanisms of Light Emission
1. Absorption
2. Spontaneous Emission
3. Stimulated Emission
1. Absorption
2. Spontaneous Emission
3. Stimulated 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
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
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:

8. Absorption
E1
E2

9. Spontaneous Emission

10. Stimulated Emission

11. Stimulated Emission