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UNIT-3 LEC-3
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ESSENTIAL COMPONENTS OF A LASER;
TYPES OF LASER,
CO 2 LASER,
Nd – YAG LASER (Doped Insulator laser),
UNIT III Lecture 3
1
Essential components of a laser system :
Active medium or Gain medium : It is the system in
which population inversion and hence stimulated
emission (laser action) is established.
Active
Medium
Pumping
Mechanism
Optical
resonator
Pumping mechanism : It is the mechanism by which
population inversion is achieved.
i.e., it is the method for raising the atoms from lower
energy state to higher energy state to achieve laser
transition.
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DIFFERENT PUMPING MECHANISMS :
i. Optical pumping : Exposure to electromagnetic radiation of
frequency  = (E2-E1)/h obtained from discharge flash tube
results in pumping Suitable for solid state lasers.
ii. Electrical discharge : By inelastic atom-atom collisions,
population inversion is established.
Suitable for Gas lasers
iii. Chemical pumping : By suitable chemical reaction in the
active medium, population of excited state is made higher
compared to that of ground state Suitable for liquid lasers.
iv. Optical resonator : A pair of mirrors placed on either side
of the active medium is known as optical resonator. One
mirror is completely silvered and the other is partially
silvered. The laser beam comes out through the partially
silvered mirror.
UNIT III Lecture 3
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Types of Lasers(Based on its pumping action) :
•Optically pumped laser
•Electrically pumped laser
• Basis of the operation mode
•Continuous wave Lasers
•Pulsed Lasers
According to their wavelength :
•Visible Region, Infrared Region, Ultraviolet Region, Microwave
Region, X-Ray Region and etc.,
According to the source :
•Dye Lasers, Gas Lasers, Chemical Lasers, Metal vapour
Lasers, Solid state Lasers, Semi conductor Lasers and other
types.
UNIT III Lecture 3
4
DYE LASERS
Laser
gain
medium
and type
Dye
lasers
Operation
wavelength(s)
390-435 nm (stilbene),
460-515 nm (coumarin
102), 570-640 nm
(rhodamine 6G), many
others
Pump
source
Other
laser,
flash
lamp
UNIT III Lecture 3
Applications
Research,
spectroscopy,
birthmark removal,
isotope separation. The
tuning range of the
laser depends on which
dye is used.
5
GAS LASERS
LASER
GAIN
MEDIUM
AND
TYPE
OPERATION
WAVELENGTH(S)
Heliumneon laser
632.8 nm (543.5 nm, 593.9
nm, 611.8 nm, 1.1523 μm,
1.52 μm, 3.3913 μm)
Argon
laser
454.6 nm, 488.0 nm, 514.5
nm (351 nm,457.9 nm,
465.8 nm, 476.5 nm, 472.7
nm, 528.7 nm)
Krypton
laser
Xenon ion
laser
PUMP SOURCE
APPLICATIONS AND NOTES
Electrical discharge
Interferometry, holography,
spectroscopy, barcode scanning,
alignment, optical demonstrations.
Electrical discharge
Retinal phototherapy (for diabetes),
lithography, confocal microscopy,
pumping other lasers.
416 nm, 530.9 nm, 568.2
nm, 647.1 nm, 676.4 nm,
752.5 nm, 799.3 nm
Electrical discharge
Scientific research, mixed with argon
to create "white-light" lasers, light
shows.
Many lines throughout
visible spectrum extending
into the UV and IR.
Electrical discharge
Scientific research.
UNIT III Lecture 3
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LASER
GAIN
MEDIUM
AND TYPE
OPERATION
WAVELENGTH(S)
PUMP SOURCE
APPLICATIONS AND NOTES
337.1 nm
Electrical discharge
Pumping of dye lasers, measuring air
pollution, scientific research. Nitrogen lasers
can operate superradiantly (without a
resonator cavity).
Carbon
dioxide laser
10.6 μm, (9.4 μm)
Transverse (high power) or
longitudinal (low power)
electrical discharge
Material processing (cutting, welding, etc.),
surgery.
Carbon
monoxide
laser
2.6 to 4 μm, 4.8 to 8.3 μm
Electrical discharge
Material processing (engraving, welding,
etc.), photoacoustic spectroscopy.
Excimer
laser
193 nm (ArF), 248 nm (KrF),
308 nm (XeCl), 353 nm (XeF)
Excimer recombination via
electrical discharge
Ultraviolet lithography for semiconductor
manufacturing, laser surgery
Nitrogen
laser
UNIT III Lecture 3
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CHEMICAL LASERS
LASER GAIN
MEDIUM AND
TYPE
OPERATION
WAVELENGTH(S)
PUMP SOURCE
Hydrogen
fluoride laser
2.7 to 2.9 μm for
Hydrogen fluoride
(<80% Atmospheric
transmittance)
Chemical reaction
in a burning jet of
ethylene and
nitrogen trifluoride
(NF3)
Used in research for laser
weaponry by the U.S. DOD,
operated in continuous wave
mode, can have power in the
megawatt range.
Deuterium
fluoride laser
~3800 nm (3.6 to
4.2 μm) (~90%
Atm. transmittance)
chemical reaction
MIRACL, Pulsed Energy
Projectile & Tactical High Energy
Laser
Chemical reaction
in a jet of singlet
delta oxygen and
iodine
Laser weaponry, scientific and
materials research, laser used in
the U.S. military's Airborne laser,
operated in continuous wave
mode, can have power in the
megawatt range.
COIL (Chemical
oxygen-iodine
laser)
1.315 μm (<70%
Atmospheric
transmittance)
UNIT III Lecture 3
APPLICATIONS
8
METAL-VAPOR LASERS
LASER GAIN
MEDIUM AND
TYPE
OPERATION
WAVELENGT
H(S)
Helium-cadmium
(HeCd) metalvapor laser
441.563 nm,
325 nm
Helium-mercury
(HeHg) metalvapor laser
567 nm, 615
nm
Helium-selenium
(HeSe) metalvapor laser
up to 24
wavelengths
between red
and UV
Copper vapor laser
510.6 nm,
578.2 nm
Gold vapor laser
627 nm
PUMP
SOURCE
Electrical
discharge in
metal vapor
mixed with
helium buffer
gas.
APPLICATIONS
Printing and typesetting applications,
fluorescence excitation examination (ie. in
U.S. paper currency printing), scientific
research.
Rare, scientific research, amateur laser
construction.
Rare, scientific research, amateur laser
construction.
Dermatological uses, high speed
photography, pump for dye lasers.
Electrical
discharge
Rare, dermatological and photodynamic
therapy uses.
UNIT III Lecture 3
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SOLID STATE LASERS
LASER GAIN
MEDIUM
AND
TYPE
Ruby laser
Nd:YAG laser
OPERATION
WAVELEN
GTH(S)
694.3 nm
1.064 μm,
(1.32 μm)
PUMP
SOURCE
APPLICATIONS
Flashlamp
Holography, tattoo removal. The first type of
visible light laser invented; May 1960.
Flashlamp,
laser
diode
Material processing, rangefinding, laser target
designation, surgery, research, pumping other
lasers
(combined with frequency doubling to
produce a
green 532 nm beam). One of the most
common high
power lasers. Usually pulsed (down to
fractions of
a nanosecond)
UNIT III Lecture 3
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LASER GAIN
MEDIUM
AND
TYPE
Er:YAG
laser
Neodymiu
m doped
Yttrium
orthovanad
ate
(Nd:YVO4)
laser
OPERATION
WAVELENGTH(S)
2.94 μm
1.064 μm
PUMP
SOURCE
APPLICATIONS
Flashlam
p, laser
diode
Periodontal scaling, Dentistry
laser
diode
Mostly used for continuous
pumping of mode-locked
Ti:sapphire or dye lasers, in
combination with frequency
doubling. Also used pulsed for
marking and micromachining.
UNIT III Lecture 3
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LASER GAIN
MEDIUM AND
TYPE
OPERATION
WAVELENGT
H(S)
PUMP
SOURCE
APPLICATIONS
Neodymium
doped yttrium
calcium
oxoborate
Nd:YCa4O(BO3
)3 or simply
Nd:YCOB
~1.060 μm
(~530 nm
at second
harmonic)
Nd:YCOB is a so called "self-frequency
doubling" or SFD laser material which is
both capable of lasing and which has
nonlinear characteristics suitable for
laser diode
second harmonic generation. Such
materials have the potential to simplify
the design of high brightness green
lasers.
Neodymium
glass
(Nd:Glass)
laser
~1.062 μm
(Silicate
glasses),
~1.054 μm
(Phosphate
glasses)
Used in extremely high power (terawatt
scale), high energy (megajoules)
multiple beam systems for inertial
Flashlamp,
confinement fusion. Nd:Glass lasers are
laser diode
usually frequency tripled to the third
harmonic at 351 nm in laser fusion
devices.
UNIT III Lecture 3
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LASER GAIN
MEDIUM AND
TYPE
Titanium
sapphire
(Ti:sapphire)
laser
OPERATION
WAVELENG
TH(S)
650-1100
nm
PUMP
SOURCE
Other
laser
APPLICATIONS
Spectroscopy, LIDAR, research.
This material is often used in
highly-tunable mode-locked
infrared lasers to produce
ultrashort pulses and in amplifier
lasers to produce ultrashort and
ultra-intense pulses.
UNIT III Lecture 3
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Cerium doped
lithium
strontium(or
calcium)
aluminum
fluoride
(Ce:LiSAF,
Ce:LiCAF)
~280 to 316 nm
Chromium
doped
chrysoberyl
(alexandrite)
laser
Typically tuned in Flashlamp, laser diode,
the range of 700 mercury arc (for CW mode
to 820 nm
operation)
Frequency quadrupled
Nd:YAG laser pumped,
excimer laser pumped,
copper vapor laser pumped.
UNIT III Lecture 3
Remote
atmospheric
sensing, LIDAR,
optics research.
Dermatological
uses, LIDAR, laser
machining.
14
SEMICONDUCTOR LASERS :
Laser gain
medium and
type
Operation
wavelength(s)
Semiconductor
laser diode
(general
information)
0.4-20 μm,
depending on
active region
material.
GaN
0.4 μm
Pump
source
Electrical
current
Applications
Telecommunications,
holography, printing,
weapons, machining,
welding, pump sources
for other lasers.
Optical discs.
UNIT III Lecture 3
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AlGaAs
0.63-0.9 μm
Electrical
current
Optical discs, laser
pointers, data
communications. 780 nm
Compact Disc player laser
is the most common laser
type in the world. Solidstate laser pumping,
machining, medical.
InGaAsP
1.0-2.1 μm
Telecommunications,
solid-state laser pumping,
machining, medical..
Vertical cavity
surface emitting
laser (VCSEL)
850 - 1500 nm,
depending on
material
Telecommunications
Hybrid silicon laser
Mid-infrared
Research
UNIT III Lecture 3
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OTHER TYPES OF LASERS :
Laser gain
medium
and type
Free
electron
laser
Operation
wavelength(s
)
Pump source
A broad
wavelength
range (about
100 nm several mm);
relativistic electron
one free
beam
electron laser
may be
tunable over a
wavelength
range
UNIT III Lecture 3
Applications
atmospheric
research, material
science, medical
applications.
17
"Nickel-like"
Samarium
laser
First demonstration
of efficient
"saturated" operation
Lasing in ultra-hot
of a sub–10 nm Xsamarium plasma
ray laser, possible
formed by double
applications in high
pulse terawatt scale resolution
X-rays at 7.3 irradiation fluences microscopy and
nm
created by
holography,
wavelength
Rutherford
operation is close to
Appleton
the "water window"
Laboratory's
at 2.2 to 4.4 nm
Nd:glass Vulcan
where observation of
laser.
DNA structure and
the action of viruses
and drugs on cells
can be examined.
UNIT III Lecture 3
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Raman
laser, uses
inelastic
stimulated
Raman
1-2 μm for
scattering in
fiber version
a nonlinear
media,
mostly fiber,
for
amplification
Other laser, mostly
Yb-glass fiber
lasers
UNIT III Lecture 3
Complete 1-2 μm
wavelength
coverage;
distributed optical
signal amplification
for
telecommunications
; optical solitons
generation and
amplification
19
CO2 LASER
Introduction :
CO2 lasers belong to the class of molecular gas
lasers.
In the case of atoms, electrons in molecules can be
excited to higher energy levels, and the distribution of
electrons in the levels define the electronic state of the
molecule.
Besides, these electronic levels, the molecules have
other energy levels.
C.K.N. Patel designed CO2 laser in the year 1964.
UNIT III Lecture 3
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Active medium :
It consists of a mixture of CO2, N2 and helium or
water vapour. The active centres are CO2 molecules
lasing on the transition between the rotational levels
of vibrational bands of the electronic ground state.
.
Optical resonators :
A pair of concave mirrors placed on either side of
the discharge tube, one completely polished and the
other partially polished.
UNIT III Lecture 3
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Pumping :
Population inversion is created by electric
discharge of the mixture.
When a discharge is passed in a tube containing
CO2, electron impacts excite the molecules to
higher electronic and vibrational-rotational levels.
This level is also populated by radiationless
transition from upper excited levels.
The resonant transfer of energy from other
molecules, such as, N2, added to the gas, increases
the pumping efficiency.
UNIT III Lecture 3
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Contd.
Nitrogen here plays the role that He plays in HeNe laser.
A carbon dioxide (CO2) laser can produce a
continuous laser beam with a power output of
several kilowatts while, at the same time, can
maintain high degree of spectral purity and spatial
coherence.
In comparison with atoms and ions, the
energy level structure of molecules is more
complicated and originates from three sources:
electronic motions, vibrational motions and
rotational motions.
UNIT III Lecture 3
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Fundamental Modes of vibration of CO2 :
Three fundamental modes of vibration for
CO2
Symmetric stretching mode (frequency 1),
Bending mode (2) and
Asymmetric stretching mode (3).
In the symmetric stretching mode, the oxygen
atoms oscillate along the axis of the molecule
simultaneously departing or approaching the
carbon atom, which is stationary.
UNIT III Lecture 3
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Contd.
In the ‘bending mode’, the molecule ceases to be
exactly linear as the atoms move perpendicular to the
molecular axis.
In ‘asymmetric stretching’, all the three atoms
oscillate: but while both oxygen atoms move in one
direction, carbon atoms move in the opposite
direction.
The ‘internal vibrations’ of carbon dioxide molecule
can be represented approximately by linear
combination of these three normal modes.
UNIT III Lecture 3
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CO2 LASER
UNIT III Lecture 3
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INDEPENDENT MODES OF VIBRATION OF CO2 MOLECULE
UNIT III Lecture 3
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The energy level diagram of vibrational –
rotational energy levels with which the main physical
processes taking place in this laser.
As the electric discharge is passed through the
tube, which contains a mixture of carbon dioxide,
nitrogen and helium gases, the electrons striking
nitrogen molecules impart sufficient energy to raise
them to their first excited vibrational-rotational
energy level.
This energy level corresponds to one of the
vibrational - rotational level of CO2 molecules,
designated as level 4.
UNIT III Lecture 3
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Contd.
collision with N2 molecules, the CO2 molecules
are raised to level 4.
The lifetime of CO2 molecules in level 4 is quiet
significant to serve practically as a metastable
state.
Hence, population inversion of CO2 molecules is
established between levels 4 and 3, and between
levels 4 and 2.
The transition of CO2 molecules between levels 4
and 3 produce lasers of wavelength 10.6 microns
and that between levels 4 and 2 produce lasers of
wavelength 9.6 microns
.
UNIT III Lecture 3
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ENERGY LEVEL DIAGRAM
UNIT III Lecture 3
30
The He molecules increase the population of level
4, and also help in emptying the lower laser levels.
The molecules that arrive at the levels 3 and 2
decay to the ground state through radiative and
collision induced transitions to the lower level 1,
which in turn decays to the ground state.
The power output of a CO2 laser increases linearly
with length. Low power (upto 50W) continuous wave
CO2 lasers are available in sealed tube
configurations.
UNIT III Lecture 3
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Contd.
•Some are available in sizes like torches for medical
use, with 10-30 W power.
• All high power systems use fast gas-floe designs.
• Typical power per unit length is 200-600 W/m.
• Some of these lasers are large room sized metal
working lasers with output power 10-20 kW.
• Recently CO2 lasers with continuous wave power
output exceeding 100 kW.
• The wavelength of radiation from these lasers is
10.6m.
UNIT III Lecture 3
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Nd: YAG Laser (Doped insulator laser) :
Lasing medium :
The host medium for this laser is Yttrium
Aluminium Garnet (YAG = Y3 Al5 O12) with 1.5%
trivalent neodymium ions (Nd3+) present as
impurities.
The (Nd3+) ions occupy the lattice sites of
yttrium ions as substitutional impurities and
provide the energy levels for both pumping and
lasing transitions.
UNIT III Lecture 3
33
Contd.
When an (Nd3+) ion is placed in a host crystal
lattice it is subjected to the electrostatic field of
the surrounding ions, the so called crystal field.
The crystal field modifies the transition
probabilities between the various energy levels
of the Nd3+ ion so that some transitions, which
are forbidden in the free ion, become allowed.
UNIT III Lecture 3
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Nd: YAG laser
UNIT III Lecture 3
35
The length of the Nd: YAG laser rod various
from 5cm to 10cm depending on the power of the
laser and its diameter is generally 6 to 9 mm.
The laser rod and a linear flash lamp are
housed in a elliptical reflector cavity
Since the rod and the lamp are located at the
foci of the ellipse, the light emitted by the lamp is
effectively coupled to the rod.
The ends of the rod are polished and made
optically flat and parallel.
UNIT III Lecture 3
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Contd.
•The optical cavity is formed either by silvering
the two ends of the rod or by using two external
reflecting mirrors.
• One mirror is made hundred percent reflecting
while the other mirror is left slightly transmitting
to draw the output
• The system is cooled by either air or water
circulation.
UNIT III Lecture 3
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ENERGY LEVEL DIAGRAM
Simplified energy level diagram for the Nd-ion in YAG showing the
principal laser transitions
UNIT III Lecture 3
38
This laser system has two absorption bands
(0.73 m and 0.8 m)
Optical pumping mechanism is employed.
Laser transition takes place between two
laser levels at 1.06 mm.
UNIT III Lecture 3
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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
obtained.
powers of over 1KW are
UNIT III Lecture 3
40
Note: Nd: Glass laser :
Glass acts as an excellent host material for
neodymium.
As in YAG, within the glass also local electric fields
modify the Nd3+ ion energy levels.
Since the line width is much broader in glass than
in YAG for Nd3+ ions, the threshold pump power
required for laser action is higher.
Nd: Glass lasers are operated in the pulsed mode
at wavelength 1.06 mUNIT III Lecture 3
41
Nd:YAG/ Nd: Glass laser 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.
UNIT III Lecture 3
42
Contd.
•YAG beams penetrate the lens of the eye to
perform intracular procedures.
•YAG lasers are used in military as range finders
and target designators.
UNIT III Lecture 3
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