1. A laser works by stimulating the emission of coherent light through a process called stimulated emission. 2. Atoms in a lasing medium are excited to a higher energy level through an external energy source, creating a population inversion where there are more excited atoms than unexcited atoms. 3. When an excited atom spontaneously decays and emits a photon, that photon can stimulate the emission of another photon of the same wavelength, phase, and direction, producing an amplified, coherent beam of light.

1. PREPARED BY:
GUIDED BY :

2. LASER is an acronym for:
L : Light
A : Amplification (by)
S : Stimulated
E : Emission (of)
R : Radiation
Term coined by Gordon Gould.

3.  Monochromatic (emit only one wave length)
 Coherent (all in same phase-improve focusing )
 Polarized (in one plane-easy to pass through
media)
 High Directionality (in one direction & non
spreading,angular speed= 1mm /meter )
 High Intensity (can focus over small area of
10^(-6))

4. Einstein explained the action of laser beam
based on quantum theory of light.
Production of laser light is a particular
consequence of interaction of radiation with
matter.
Interpretation of interaction is done on basis of
ideas related to energy levels of concerned
system for which light is to be obtained.

5. There are three possible ways
through which interaction of
radiation and matter can take
place :
1.
2.
3.

6. Transition of atom from Ground-State (E1) to higher
energy state(E2) on absorption of energy, supplied
externally.
E2 E2
E=hv
E1 E1
Before Absorption

7. After excitation, atom will spontaneously transit from
higher energy excited state to ground state.While this,it
emits photon.
atom in exited state
E2
E1
Before emission After Emission

8.  Emission of photon whenever an atom transits from a
higher energy exited state to lower energy under
influence of an external agency,i.e. Inducing photon.
 It is principle of laser action.

9. TWO NECCESSARY CONDITIONS FOR
STIMULATED EMISSION :
1.Metastable State: Energy levels where life time of
atoms is of order 10^(-3) to 10^(-2) second.
2.Powerful source of energy

10.  Population Inversion: State of achieving
more number of atoms in the exited state compared
to ground state. [N2 > N1]
 Life Time: Limited time for which a particle
remiains in the exited state. It is about nano second.

11. This is the basic material in
which atomic and molecular transitions take place
leading to laser action. It is the medium where the
stimulated emission take place.

12. With the help of energy
source the system can be raised to an excited state,
with the help of this source the no. of atoms in higher
energy state may be increased and hence the
population inversion is achieved.
Set of mirrors at
the ends of which are silvered one end being
completely silvered at which the other is partially
silvered Photons are emitted parallel to the axis of the
active medium undergo multiple reflections between
them .So, the light intensity can be increased.

15. 1. Energy is applied to a medium raising electrons to an
unstable energy level.
2. These atoms spontaneously decay to a relatively long-
lived, lower energy, metastable state.
3. A population inversion is achieved when the majority of
atoms have reached this metastable state.
4. Lasing action occurs when an electron spontaneously
returns to its ground state and produces a photon.
5. If the energy from this photon is of the precise
wavelength, it will stimulate the production of another
photon of the same wavelength and resulting in a
cascading effect.
6. The highly reflective mirror and partially reflective mirror
continue the reaction by directing photons back through
the medium along the long axis of the laser.
7. The partially reflective mirror allows the transmission of a
small amount of coherent radiation that we observe as
the “beam”.
8. Laser radiation will continue as long as energy is applied
to the lasing medium.

16.  MILITARY APPLICATIONS:
1.Find Target
An infrared camera on the laser continuously scans a 6 to
10-mile radius around the airport for suspicious heat
emissions. When it finds a plume, it relays the coordinates
to an identification and tracking system, which is also on
the unit.
2. Destroy Missile
The laser-beam cannon emits a burst of intense light
aimed at the missile’s most vulnerable spot, usually the
explosives compartment. Simultaneously, it sends a signal
to airport control tower to give authorities a fix on the
origin of the rocket.

17. In industry
◦ to drill tiny holes in hard materials,
◦ for welding and machining,
◦ for lining up equipment precisely, especially in
inaccessible places.
In medicine
◦ to break up gallstones and kidney stones,
◦ to weld broken tissue (e.g. detached retina)
◦ to destroy cancerous and precancerous cells; at the same time, the heat
seal off capillaries,
◦ to remove plaque clogging human arteries.
 used to measure blood cell diameter
 fibre-optic laser catheter is in the treatment of bleeding
ulcers.
 can photocoagulate blood
 can also be used for dental treatment