Prepared by:-

Kajal barad(151080106002)

Guided by:-

Medha shah

LASER

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.

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!

Diode Laser

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.

Fibre Optics Communication

3 Mechanisms of Light Emission

1. Absorption2. Spontaneous Emission3. Stimulated Emission

For atomic systems in thermal equilibrium with their surrounding, the emission of light is the result of:

AbsorptionAnd 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 emissionIt is an important process for laser action

Therefore 3 process of light emission:

Absorption

E1

E2

Spontaneous Emission

Stimulated Emission

Stimulated Emission