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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