Laser_2nd BPT_ 1st Class

8/13/2019 Laser_2nd BPT_ 1st Class

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LASERLIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATIONS

Dr. Amitesh NarayanMPT/Ph.D


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Laser: Introduction

Metastable state:

Excited electron loses energy via a state in which

the molecule/atom is very nearly stable, enabling

electrons to spend relatively long time, before

making transition to the ground state.


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Laser: Introduction

Electrons may leave this metastable state

spontaneously or be triggered by a photon of

precisely the same energy to fall to the ground state.

called

Stimulated emission.


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Laser: Stimulated Emission

Stimulated Emission allows production of

Light amplification by stimulated emission ofradiations (LASER)


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LASER: Physical Properties

1. Monochromatic, i.e. of one wavelength only.

2. Coherent: means all the peaks and troughs of the magnetic

and electric fields occurs at the same time (temporal) and

travel in the same direction (spatial).

3. Due to spatial coherence and method of laser radiationproduction, LASER rays appears in a narrow, parallel beam.


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LASER: Physical Properties Comparision with other rays

Non-coherent infrared and visible radiations are like a

crowd of people all in different clothes, walking in

different ways and out of step.

Laser radiationis like a column of soldiers all marching

in step (in phase), wearing the same uniform

(monochromatic) and going in exactly the same

direction (spatial coherence).


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LASER: Production

Lasers can be produced from solids, liquids

and gases under the right conditions.


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RUBY Laser

Early lasers

Synthetic ruby rod, about 10 cm long and of 1 cm

diameter with a xenon flash tube wound round it in a

spiral fashion.

Ends of the rod are flat and silvered to act as

reflectors, but one is made only partially reflecting.


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RUBY Laser

A powerful light flash from the xenon tube provides

photons with energy to excite the molecules of the

ruby rod to high energy levels.

After a very short time in the high-energy band, many

spontaneous transitions occur to a metastable state

in which the molecules remain for much longer

periods.


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RUBY Laser


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Helium-Neon Laser

Consist of a tube containing Helium and Neon gases at

low pressureand is surrounded by a flashgun tube.

Excitation causes different energy levels between

these two atomsand a transfer of energy giving off a

photon of a wavelength equal to the energy gap of

632.8 nm.


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Infrared Laser

Carbon dioxide is used to provide high-intensity (up to 20000 W) infrared lasers for

the surgical destruction of tumors.


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Chemical lasers

In Chemical lasers, energy source is a chemical

reaction, are more efficient than ordinary

lasers which only convert around 2% of their

energy to laser radiation.


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Organic Laser

In Organic lasers, complex organic dye is

utilized, which produces radiations at a

predetermined wavelength.


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Semiconductor Laser

Material used are Gallium- Aluminium -Arsenide (Ga-Al-

As).

Materials: Diodes.

Excitation is effected by an electric potential affecting

electron- hole pairing in the crystal lattice.


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Semiconductor Laser

Stores energy in the material, which can be

released in the form of identical photons.

Photons: reflected to and fro in the material, to

be ultimately emitted as a laser beam.


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Semiconductor Laser

Absorption and emission of photons: (a) absorption; (b) emission; (c) stimulated

emission.


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Semiconductor Laser

Semiconductor Lasers are

a. relatively cheap to construct,

b. quite robust,

c. can be made to be very small, and

d. emit a predetermined wavelength by varying the

relative proportions of gallium to Aluminium.


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Examples of Laser


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Classification of Laser

Laser_2nd BPT_ 1st Class

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