2. CHARACTERISTICS of LASER LIGHT
Monochromatic- “single colour”
Coherent- waves are “in phase”
Highly Directional- resulting in very concentrated light
energy
Highly Intense and Bright
Focusability- Can be focused to an extremely fine spot of
diameter of just 0.0006cm (He-Ne Laser)
NOTE:
You can be burned by a 60 Watt light bulb, but a 60 Watt laser
can cut through wood!
6. Linear amplification through Population Inversion
Stationary state of population inversion. It is dynamic but not static
Pumping
Pumping
Spontaneous emission
or/and collisions
8. Nd:YAG Laser
It is a four level and solid state laser system in which energy levels of neodymium
ion take part in laser emission.
Solid lasers use ions suspended in a crystalline matrix to produce laser light. The
ions or dopants provide the electrons for excitation, while the crystalline matrix
propagates the energy between ions.
It became popular in 1960`s
Nd:YAG lasers operate in both pulsed and continuous mode
The lasing medium is red in colour, isotropic crystal Y2Al5O12 (Yttrium-Aluminum
Garnet - YAG).
When used in a laser, about 1-1.5% of the Yttrium is replaced by
Neodymium. The energy levels of the Nd3+ ion are responsible for the lasing
action. The rare earth ion does not affect the crystal structure due to similar size
Ytterbium, erbium, chromium etc. are also used as dopant in YAG for laser
operation
9. Construction
Essential parts of laser:Yttrium Aluminium Garnet in which 1.5% of neodymium ions are doped as impurities. Nd3+ is the
lasing ion.
Two end mirrors M1 (total reflector) & M2 (output coupler)
Excitation is achieved by krypton or xenon arc lamps
Nd : YAG laser rod has a length of about 5-10 cm with a diameter 6-9mm. It is kept at one foci of an
elliptical glass tube.
Krypton arc lamp , the optical source is placed at the other foci of the glass tube. It is provided with
necessary power supply arrangement.
Mirrors M1 (total reflector) & M2(output coupler) act as a resonant cavity to produce stimulated and
amplification process.
10. Population inversion results from shining light on this crystal. If the light is
intense enough, atoms within the crystal will absorb this light and make
transition from ground state into the absorption bands. This is often done with
a krypton flash lamp.
The Nd-YAG laser is normally shaped as cylindrical crystal. The crystal forms
the laser cavity and has reflective ends - one coated so that it is 100%
reflective, and the other is either sufficiently reflective, or is coated to allow
only part of the amplified light to pass which is enough for feed-back so that
oscillation may occur.
11. YAG Crystal Rod
Rods of Nd:YAG crystal exhibit excellent properties of conduction of heat.
As such, they are better for laser operations involving high repetition rate.
But these rods have one limitation that the growth of these crystals is
possible only for making small rods of the size of 10cm in length and 1cm
in diameter.
13. Working of Nd:YAG laser
When arc lamp is energised it gives out
radiations
Nd+3 ions get excited to higher energy
levels by absorbing 0.73 μm and 0.80μm
from the input radiations.(white light)
Nd+3 ions can stay for a duration of about
10-8 sec in the excited energy levels.
These
ions undergo non radiative
transitions to reach the meta-stable state
E3.
Laser output of wavelength 1.06 μm
(Infrared) is obtained from E3 to E2
transition.
As continuous pumping is done by arc
lamp, laser output is in the form of CW
mode.
Radiative transitions: Transitions
between energy levels that occur with
the absorption or emission of
radiation
Non-radiative
transitions:
occur
without the absorption or emission of
radiation
14. OUTPUT CHARACTERISTICS :
The laser output is in the form of pulses with
higher repetition rate
Xenon flash lamps are used for pulsed output.
Nd: YAG laser can be operated in CW mode
also using tungsten-halide incandescent lamp for
optical pumping.
Continuous output powers of over 1KW are
obtained.
16. Facts about Nd:YAG laser
The output in the infrared region of the Nd:YAG laser can be
converted to visible region ( =400-700nm) by adopting
frequency-doubling techniques and they are used in several
commercial applications.
The system is so compact and portable that it can be even
contained in a very small box one forth the size of a briefcase.
A recent development in Nd:YAG system is by using
semiconductor laser output to pump the atoms of Nd3+ ions
directly to the metastable state.
The ability of semiconductor lasers to convert electrical
energy to photons is quite high. As such, YAG laser can be
pumped with simple power supplies-even torch batteries.
17. Applications of Nd:YAG Laser:
Medicine
In oncology, it is used to remove skin cancer
It is used in ophthalmology to correct posterior capsular pacification, a
complication of cataract operation
Cosmetic medicine
Dentistry: It is used for soft tissue surgeries in the oral cavity
Manufacturing
For engraving, etching, or marking a variety of metals and plastics.
Cutting and welding steel and various alloys.
For automotive applications (cutting and welding steel) the power levels
are typically 1-5 kW
Military
Military surplus Nd:YAG laser fires through a collimator, focusing the
beam, which blasts a hole through a rubber block, releasing a burst of
plasma.
The Nd:YAG laser is the most common laser used in military as laser
rangefinders
18. Some more applications:
These lasers are used in many scientific applications
which involve generation of other wavelengths of light.
The important industrial uses of YAG and glass lasers
have been in materials processing such as welding,
cutting, drilling.
Since 1.06 m wavelength radiation passes through
optical fibre without absorption, fibre optic endoscopes
with YAG lasers are used to treat gastrointestinal bleeding.
YAG beams penetrate the lens of the eye to perform
intracular procedures.
YAG lasers are used in military as range finders and
target designators.
19. LIDAR (LIght Detection And Ranging)
The laser system that is employed for monitoring the nature of
environment is called LIDAR.
First a pulsed beam is transmitted into the atmosphere. The particles
that are present in the atmosphere scatter the radiation.
The scattered radiation is picked up by a receiver and given to detector.
The background sunlight is removed by specially designed filter elements.
A photo detector measures the time dependence of the intensity of the
back-scattered laser beam. This time difference is a function of the light
from which the particle has scattered the light and conversion of this
function into meters or any other unit of measurement is easy.
Using LIDAR, it is also possible to study the concentrations and sizes of
the aerosols present in the atmosphere. This helps in studies involving air
pollution. Atmospheric conditions, which get affected by diffusion of
particle, clouds, fog, smog, etc., can be studied using LIDAR.
The results from a sensitive laser device has better resolution and
clarity.
20. DETECTION OF LEAKAGE IN GAS PIPELINE Using
LIDAR
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