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 Laser is a device which can produce a highly intense,
highly choerent, more directional and highly
monochromatic beam.
 Laser is an acronym for light amplification by
stimulated emission of radiation.
 In laser intensity of light is amplified by a process
called stimulated emission.
 Lasers are optical phenomena which find major
application in various fields.
 Example : Fiber Optic Communication,Industries,etc.
 Lasers are more poweful radiation than ordinary light
radiation.

 The following characteristics , distinguishes a
laser beam from an ordinary light. They are four
type.
The wave trains which are identical in
phase and direction are called coherent waves.
 Since all the constituent photons of laser
beam possess same energy, momentum and
propagate in same direction, laser beam is said
to be highly coherent.

:
It has ability to focus over a small area
of 10⁻⁶ cm².
:
Laser travels as a parallel beam it
can travel over a long distance without
spreading.The angular spread of a laser beam is 1
mm/meter.
:
The light from a normal
monochromatic source spreads over a rang of
wavelength of the order 100 mm but the spread is of
the order of 1 mm for laser.

1. Induced Absorption :
 Let the atom be initially in the lower state E₁.
 If a photon of energy h v is incident on the atom in
the lower state, the atom absorbs the incident
photon and gets excited to the higher energy state
E₂.
 This process is called induced aborption.
Induced Absorption

2. Spontaneous Emission :
Emission of a light photon
takes plce through an inducement i.e. by an
extemal photon.
 It is not a random process.
 The photons get multiplied through chain
reaction.
 It is a controllable process.
 It is more intense.
 Monochromatic radiation.
Spontaneous Emission

3. Stimulated Emission :
Emission of light photon takes
place immediately without any inducement.
 It is a random process.
 The photons do not get multiplied through chain
reaction.
 It is an uncontrollable process.
 It is less intense.
 It is a polychromatic radiation.
Stimulated Emission

Active Medium :
oThis is a four level solid state laser system.
oYttrium Aluminium Garnet(Y3Al5O12),commonly
known as YAG,doped with neodymium ions Nd³⁺ is
the active medium.
oThe neodymium inos Nd³⁺ are the active centers.
Resonator Cavity :
oThe end face of Nd:YAG rod ground polished and
silvered to act optical resonator mirrors using tow
external reflecting mirrors M₁ and M₂.

Optical Pumping :
oA xenon flash lamp or a krypton flash lamp is
used as a pumping source.
Construction :
oThe schematic diagram of a Nd:YAG is shown in
here

Applications Of Nd:YAG :
 These laser are widely used for
cutting,drilling,welding and surface hardening
of the industrial products.
 Military as range finder and as target
designations.
 Medical field for cataract surgery etc.
 Long haul communication.
 Study of inertial confinement fusion.

 Some of the Applications Of Laser in various
fields are listed below.
1) In Industry :
 Welding and melting.
 Cutting and drilling holes.
 To test quality of materials.

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Lasers

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