LASER systems presentation LASER and optics Physics #science #research #study material #work #education #knowledge #helping material #students

1. 1
 ESSENTIAL COMPONENTS OF A LASER;
 TYPES OF LASER,
 CO 2 LASER,
 Nd – YAG LASER (Doped Insulator laser),
LASER SYSTEMS

2. 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.
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.
Active
Medium
Pumping
Mechanism
Optical
resonator

3. 3
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.

4. 4
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.

5. 5
DYE LASERS
Laser gain
medium
and type
Operation wavelength(s)
Pump
source
Applications
Dye lasers
390-435 nm (stilbene),
460-515 nm (coumarin
102), 570-640 nm
(rhodamine 6G), many
others
Other
laser,
flash
lamp
Research, spectroscopy,
birthmark removal,
isotope separation. The
tuning range of the laser
depends on which dye is
used.
Stilbene (Isomer): A compound that exists in forms having
different arrangements of atoms but the same molecular
weight.
Coumarin is a fragrant organic chemical compound in the
benzopyrone chemical class, which is a colorless crystalline
substance in its standard state. It is a natural substance
found in many plants.

6. 6
GAS LASERS
LASER
GAIN
MEDIUM
AND
TYPE
OPERATION
WAVELENGTH(S)
PUMP SOURCE APPLICATIONS AND NOTES
Helium-
neon
laser
632.8 nm (543.5 nm,
593.9 nm, 611.8 nm,
1.1523 μm, 1.52 μm,
3.3913 μm)
Electrical discharge
Interferometry, holography,
spectroscopy, barcode
scanning, alignment, optical
demonstrations.
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)
Electrical discharge
Retinal phototherapy (for
diabetes), lithography, confocal
microscopy, pumping other
lasers.
Krypton
laser
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.
Xenon
ion laser
Many lines throughout
visible spectrum
extending into the UV
and IR.
Electrical discharge Scientific research.

7. UNIT III Lecture 3
7
LASER
GAIN
MEDIUM
AND TYPE
OPERATION WAVELENGTH(S) PUMP SOURCE APPLICATIONS AND NOTES
Nitrogen
laser
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
monoxid
e 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

8. 8
LASER GAIN
MEDIUM AND
TYPE
OPERATION
WAVELENGTH(S)
PUMP SOURCE APPLICATIONS
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
COIL (Chemical
oxygen-iodine
laser)
1.315 μm (<70%
Atmospheric
transmittance)
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.
CHEMICAL LASERS

9. 9
LASER GAIN
MEDIUM AND
TYPE
OPERATION
WAVELENGTH
(S)
PUMP
SOURCE
APPLICATIONS
Helium-cadmium
(HeCd) metal-
vapor laser
441.563 nm,
325 nm
Electrical
discharge in
metal vapor
mixed with
helium buffer
gas.
Printing and typesetting applications,
fluorescence excitation examination (ie. in
U.S. paper currency printing), scientific
research.
Helium-mercury
(HeHg) metal-
vapor laser
567 nm, 615
nm
Rare, scientific research, amateur laser
construction.
Helium-selenium
(HeSe) metal-
vapor laser
up to 24
wavelengths
between red
and UV
Rare, scientific research, amateur laser
construction.
Copper vapor
laser
510.6 nm,
578.2 nm
Electrical
discharge
Dermatological uses, high speed
photography, pump for dye lasers.
Gold vapor laser 627 nm
Rare, dermatological and photodynamic
therapy uses.
METAL-VAPOR LASERS

10. LASER GAIN
MEDIUM AND
TYPE
OPERATION
WAVELENGTH(S)
PUMP
SOURCE
APPLICATIONS
Ruby laser 694.3 nm Flashlamp
Holography, tattoo removal. The first
type of visible light laser invented; May
1960.
Nd:YAG laser
1.064 μm, (1.32
μm)
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)
10
SOLID STATE LASERS

11. 11
Er:YAG
laser
2.94 μm
Flashlamp,
laser diode
Periodontal scaling, Dentistry
Neodymium
doped
Yttrium
orthovanad
ate
(Nd:YVO4)
laser
1.064 μm 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.
LASER GAIN
MEDIUM AND
TYPE
OPERATION
WAVELENGTH(S)
PUMP
SOURCE
APPLICATIONS

12. 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)
laser
diode
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
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
(Phosphat
e glasses)
Flashlamp
, laser
diode
Used in extremely high power (terawatt
scale), high energy (megajoules)
multiple beam systems for inertial
confinement fusion. Nd:Glass lasers are
usually frequency tripled to the third
harmonic at 351 nm in laser fusion
devices.
12

13. LASER GAIN
MEDIUM AND
TYPE
OPERATION
WAVELENGT
H(S)
PUMP
SOURCE
APPLICATIONS
Titanium
sapphire
(Ti:sapphire)
laser
650-1100
nm
Other
laser
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.
13

14. Cerium doped
lithium
strontium(or
calcium)
aluminum
fluoride
(Ce:LiSAF,
Ce:LiCAF)
~280 to 316 nm
Frequency quadrupled
Nd:YAG laser pumped,
excimer laser pumped,
copper vapor laser pumped.
Remote atmospheric
sensing, LIDAR,
optics research.
Chromium
doped
chrysoberyl
(alexandrite)
laser
Typically tuned in
the range of 700
to 820 nm
Flashlamp, laser diode,
mercury arc (for CW mode
operation)
Dermatological uses,
LIDAR, laser
machining.
14

15. 15
Laser gain
medium and
type
Operation
wavelength(s)
Pump
source
Applications
Semiconductor
laser diode
(general
information)
0.4-20 μm,
depending on
active region
material.
Electrical
current
Telecommunications,
holography, printing,
weapons, machining,
welding, pump sources
for other lasers.
GaN 0.4 μm Optical discs.
SEMICONDUCTOR LASERS :

16. 16
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. Solid-
state 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

17. 17
Laser gain
medium and
type
Operation
wavelength(s)
Pump source Applications
Free electron
laser
A broad
wavelength
range (about
100 nm - several
mm); one free
electron laser
may be tunable
over a
wavelength
range
relativistic electron
beam
atmospheric
research, material
science, medical
applications.
OTHER TYPES OF LASERS :

18. 18
"Nickel-like"
Samarium
laser
X-rays at 7.3
nm
wavelength
Lasing in ultra-hot
samarium plasma
formed by double
pulse terawatt scale
irradiation fluences
created by
Rutherford Appleton
Laboratory's
Nd:glass Vulcan
laser.
First demonstration
of efficient
"saturated" operation
of a sub–10 nm X-ray
laser, possible
applications in high
resolution
microscopy and
holography,
operation is close to
the "water window"
at 2.2 to 4.4 nm where
observation of DNA
structure and the
action of viruses and
drugs on cells can be
examined.

19. 19
Raman laser,
uses
inelastic
stimulated
Raman
scattering in
a nonlinear
media,
mostly fiber,
for
amplification
1-2 μm for
fiber version
Other laser, mostly
Yb-glass fiber lasers
Complete 1-2 μm
wavelength
coverage;
distributed optical
signal amplification
for
telecommunications
; optical solitons
generation and
amplification

20. 20
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.

21. 21
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.

22. 22
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.

23. 23
Contd.
Nitrogen here plays the role that He plays in He-Ne
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.

24. 24
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.

25. 25
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.

26. 26
CO2 LASER

27. 27
INDEPENDENT MODES OF VIBRATION OF CO2 MOLECULE

28. 28
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.

29. 29
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.

30. 30
ENERGY LEVEL DIAGRAM

31. 31
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.

32. 32
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.

33. 33
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.

34. 34
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.

35. 35
Nd: YAG laser

36. 36
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.

37. 37
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.

38. 38
ENERGY LEVEL DIAGRAM
Simplified energy level diagram for the Nd-ion in YAG showing the
principal laser transitions

39. 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.

40. 40
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.

41. UNIT III Lecture 3
41
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 m

42. 42
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.

43. 43
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.

44. THE END