2. Introduction
In early 1960s Quantum physics made
enormous contribution to technology by
introducing a Laser a device that creates
an intense beam of light is called as laser
beam.
The word laser is an acronym that stands
for “light amplification by the stimulated
emission of radiation”.
Lasers are essentially highly directional,
highly intense, highly monochromatic and
highly coherent optical sources.
3. • Stimulated emission was postulated by
Einstein as early as in 1917.
• In 1960 , a solid state ruby laser is
developed by Maiman on this
principle.
• In 1961, a gas state He-Ne laser is
developed by Ali javan and others
in Bell telephone laboratory.
4. Working Principle
Laser action is quantum process that occur in
a material medium if its exposed radiation of
photon of energy hv.
Atoms and molecules have discrete energy
level when they absorbs or emit the photon
they make transition between energy level.
There are two energy level one in ground state
and other is excited state these level are
quantized energy level there is no intermediate
level the atoms are present one of these level
and when beam of Photon particles incident on
it there is certain phenomenon occurs.
6. There is two energy level E1 is represents
ground state & E2 will represents the excited
state.
The atoms in ground state are remain ground
state until an external radiation incident on it.
The Photon with appropriate frequency is
incident on atom which is ground state they
are excited on the excited state.
This is called as absorption
According to principle of conservation of
energy.
hv = E2 - E1
Absorption
8. In Spontaneous emission atoms are in
excited level they are jump on the
ground state by emitting the
electromagnetic radiation.
The frequency of emitted radiation v is
directly proportional to the energy
differences between two energy level
or energy difference is inversely
propotional to wavelength of radiation
from v = c/λ
Spontaneous Emission
10. In Stimulated emission the external
triggering is required to decay the
atoms in ground state.
This phenomenon which is studied by
Einstein in 1917.
According to this phenomenon the
photon which is incident the atoms
whose are in excited state when they
are transition to the ground state they
emit the photon which is same phase
with incident radiation photon.
Stimulated Emission
11. Hence we get monochromatic,
coherent source of light from LASER.
Thus along with an incident triggering
photon one more photon is also
produced if this two photon are further
used in triggering more and more
excited atoms one identical multiple
photon 4, 8, … etc. such amplification
is called as amplification of light by
stimulated emission of radiation.
Stimulated Emission
12. Few points discussed
• At thermal equilibrium condition nos. atom
in the ground state is larger than exited
state in that case there incident radiation
incident on the atoms so that there is
absorption takes place hence its called as
attenuation of light
• But in non equilibrium condition the nos. of
atom in the exited state is larger than
ground state so when radiation incident on
it result in stimulated emission is called as
Optical amplification.
13. • Einstein showed that both the process like
stimulated absorption and stimulated
emission has equal probability.
• According to Boltzman Distribution Law :
N2/N1 = exp [-(E2 – E1)/kT]
N2 :- Nos. of atom in excited state.
N1 :- Nos. of atom in ground state.
E2 :- Energy level of excited level
E1 :- Energy level of ground level
k :- Boltzman Constant
T :- Temperature
14. •Case :- I
If T is positive E2 > E1 therefore
N2 < N1 Absorption Dominates.
•Case :- II
If T is Negative N2 > N1
Stimulated Emission Dominates.
16. Population Inversion
• To increases the nos. of atom in excited
state than ground state N2 > N1 for laser
action such process is called as population
Inversion.
• To raise atoms from ground state to excited
state by external energy source is called as
pumping
17. Active Medium
The Active medium is the material
used in a laser.
The Active is consists of collection
of atoms molecule or ions.
The active medium is solid liquids
or gaseous state
19. In The process of Optical amplification is
achieved by placing the active medium in
Two mirror M1 & M2 called as optical
reflector such system of mirrors used to
obtain optical feedback is called as mirror
cavity resonator or optical resonator.
22. • Laser light high monochromatic light source
than conventional light source .
• Eg. The Spectral Width Neon light is
approximately 5A0 whereas the He – Ne
Laser gives spread of 10-8 A0 at 6328A0 i.e.
Laser light highly monochromatic.
• Laser light spectral width of the order 10-6 A0
which is extremely small as compared with
the width of the order 0.1 A0 of sodium light.
• Light from conventional source is more or
less sharp but for laser light is sharp
Monochromaticity
24. • Laser light is highly coherent.
• The stimulated emission give rise of
coherence of radiated beam.
• The emitted photon train of laser light which
maintain constant phase.
• When the two wavetrain interfere they
producing steady interference.
• On the other hand ordinary light whose
coherence length of wave train emitted by a
light less than meter.
Coherence
25. • Laser light is produced highly intense beam
than conventional light source.
• Laser light is emitted by continues
wavetrain which is highly intense is focused
on very small area.
•I = (10/λ)2 P
• The unit of Intensity W/m2
Intensity & Power
26. • Laser light is highly directional than
ordinary light source they travel a greater
distance without divergence or spreading.
• The divergence can be less than 10-5 radians
the width is also narrow so they should
focus extremely sharp focus.
• On the other hand ordinary light diverges
more as it propagates
• The directionality of laser is measured in
terms of full angle beam divergence
Directionality
30. • Laser is used for various metallic welding
purposes when laser is focus on small area
its start melt because of high temperature
so the metal can easily join with another
metal.
• Eg. CO2 Laser at 10.6 µm have a power of
order 6kW it welding 0.25 inch thick steel its
cheaper than ordinary welding.
• Nd : YAG laser 1.06 µm with output 100
mJ/pulse is more compact because of low
peak power pulses of 10-3 to 10-2s width and
suitable for welding.
Laser Welding
31. • Laser is also used for cutting purpose of
material like textiles industries for cutting
cloth, in aeroplane industries for cutting
aluminium sheet, wood plastic glass
ceramics. Using a jet with the laser the
efficiency of laser cutting can be increased.
• This process of High accuracy & fine
precision.
Laser Cutting
36. • Holography is wide application in
holographic, Interferometry, holographic
microscope etc a hologram is for data
storage its also used to recording three
dimensional image and cinemas.
Application of Holography
37. • Laser is used in medical purpose because its high
precision and accuracy.
• He – Ne laser is trophic Ulcer treatment and
preparation of hologram.
• CO2 Laser has application in brain oviduct and
spinal surgery.
• Argon Laser is used in angioplasty brain and eye
surgery.
• Nitrogen Laser is used in DNA analysis & genetic
engineering
Laser in Medical
