1.
Gas Laser
ME6805
Submitted by:
Rahul Kaswan(1801071)
Shekhar Kumar(1801024)
Shashank Dixit(1801044)

2.
Contents
 Introduction of Laser
 Principal of Laser
 Types of Laser
 Properties of Laser
 Gas laser
1.He-Ne Laser
2. CO2 gas Laser
3. N2 gas Laser
4. Argon gas laser

3.
LASER?
 The term "laser" originated as an acronym for "light amplification by stimulated
emission of radiation“
 A laser is a device that emits light through a process of optical amplification based
on the stimulated emission of electromagnetic radiation.

4.
 In absorption, energy is absorbed by an atom, the electrons are excited into
vacant energy shells.
 In spontenous emission, the atom decays from level 2 to level 1 through the
emission of a photon with the energy hv. It is a completely random process.
 In stimulated emission, atoms in an upper energy level can be triggered or
stimulated in phase by an incoming photon of a specific energy.

5.
Stimulated Emission
 The stimulated photons have unique properties:
– In phase with the incident photon
– Same wavelength as the incident photon
– Travel in same direction as incident photon
This Photo by Unknown Author is licensed under CC BY-SA

6.
Types of Laser
Lasers are classified into 4types based on the types of laser medium used:

7.
Properties of Laser
 Monochromatic: Concentrate in a narrow range of wavelengths (one
specific colour ).
 Coherent: All the emitted photons bear a constant phase relationship
with each other in both time and phase.
 Directional: A very tight beam which is very strong and concentrated.

8.
Population Inversion
 A state in which a substance has been energized, or excited to specific
energy levels.
 More atoms or molecules are in a higher excited state.
 The process of producing a population inversion is called pumping.
 Examples: →by lamps of appropriate intensity
→by electrical discharge

9.
Gas Laser?
 A gas laser is a laser in which an electric current is discharged through a gas to
produce coherent light.
 It is operated on the principle of converting electrical energy to a laser light output.
Types of Gas laser
1.He – Ne laser
2.Carbondioxide gas laser
3.Nitrogen gas laser
4.Argon gas laser

10.
He-Ne Laser  A helium-neon laser, usually called a He-
Ne laser, is a type of small gas laser.
 He-Ne lasers have many industrial and
scientific uses, and are often used in
laboratory demonstrations of optics.
 He-Ne laser is a four-level laser.
 Its usual operation wavelength is 632.8
nm, in the red portion of the visible
spectrum.
 It operates in Continuous Working (CW)
mode.
The Helium-Neon laser was the first
continuous laser.
It was invented by Javan et. al. in
1961.

11.
Construction of He-Ne laser
 The setup consists of a discharge tube of length 80 cm and
bore diameter of 1.5cm.
 The gain medium of the laser, as suggested by its name, is a
mixture of helium and neon gases, in a 5:1 to 20:1 ratio,
contained at low pressure (an average 50 Pa per cm of cavity
length ) in a glass envelope.
 The energy or pump source of the laser is provided by an
electrical discharge of around 1000 volts through an anode
and cathode at each end of the glass tube. A current of 5 to
100 mA is typical for CW operation.
 The optical cavity of the laser typically consists of a plane, high-
reflecting mirror at one end of the laser tube, and a concave
output coupler mirror of approximately 1% transmission at the
other end.

12.
Energy Level Diagram

13.
Working :
 A description of the rather complex HeNe excitation process
can be given in terms of the following four steps.
 (a)When the power is switched on, An energetic electron
collisionally excites a He atom to the state labeled 2 1S0 . A
He atom in this excited state is often written He*(2 1S0), where
the asterisk means that the He atom is in an excited state.
 (b) The excited He*(2 1S0) atom collides with an unexcited
Ne atom and the atoms exchange internal energy, with an
unexcited He atom and excited Ne atom, written Ne*(3S2),
resulting. This energy exchange process occurs with high
probability only because of the accidental near equality of
the two excitation energies of the two levels in these atoms.
Thus, the purpose of population inversion is fulfilled.

14.
Working
 When the excited Ne atom passes from metastable state(3s) to
lower level(2p), it emits photon of wavelength 632 nm.
 This photon travels through the gas mixture parallel to the axis of
tube, it is reflected back and forth by the mirror ends until it
stimulates an excited Ne atom and causes it to emit a photon of
632nm with the stimulating photon.
 The stimulated transition from (3s) level to (2p) level is laser
transition.
 This process is continued and when a beam of coherent radiation
becomes sufficiently strong, a portion of it escape through
partially silvered end.
 The Ne atom passes to lower level 1s emitting spontaneous
emission. and finally the Ne atom comes to ground state through
collision with tube wall and undergoes radiationless transition.

15.
Application of He-Ne Laser
 The Narrow red beam of He-Ne laser is used in supermarkets to read bar
codes.
 The He- Ne Laser is used in Holography in producing the 3D images of
objects.
 He-Ne lasers have many industrial and scientific uses, and are often used in
laboratory demonstrations of optics.

16.
PROS & CONS
Advantages
 High coherence length.
 Stable central wavelength.
 High spectral purity. .
 Good beam quality and alignment.
 Low-cost.
Disadvantage
 Short life-time.
 Long warm-up time..
 Low output power.
 Very bulky.
 High voltage.

17.
Nitrogen LASER
(N2 LASER)
Contents→
1.INTRODUCTION
2.WORKING
3.APPLICATION
1

18.
INTRODUCTION
➢ A nitrogen laser is a gas laser operating in the ultraviolet
(UV) range by using molecular nitrogen as its gain
medium. Nitrogen lasers were first developed in 1963.
➢ Nitrogen lasers operate based on a fast electrical
discharge through nitrogen gas. The nitrogen gas can
be supplied through a gas cylinder, or from liquid
nitrogen. The laser light emitted is in the UV range, with a
short pulse width and high intensity.
2

19.
WORKING
The nitrogen laser uses electricity
to excite
the nitrogen. When an electric
spark crosses a
spark gap in the laser, the
electrons hit the
nitrogen atoms in air thereby
exciting them
into a metastable state. When a
photon with a
wavelength of 337 nm passes the
excited
nitrogen atoms, stimulated
emission occurs
and a laser state is generated.
3

20.
Equil. Distance
4

21.
APPLICATION
❖ Transverse optical pumping of dye lasers.
❖ Treatment of non-healing wounds, pulmonary tuberculosis, etc.
 Nitrogen lasers can be used for a wide range of
applications in the UV-visible region. They can be
easily coupled to a microscope for carrying out
experiments in life science laboratories. They are also
efficient sources for laser-induced fluorescence and
photochemistry and general spectroscopy.
5

22.
DISADVANTAGE
 The Beam quality of the Nitrogen laser is poor.
 The divergence of Nitrogen laser is large as compared
to the divergence of other lasers.
 The output power is low.
 The efficiency of a Nitrogen laser is low.
6

23.
CO2 LASER
Contents→
1.INTRODUCTION
2.CONSTRUCTION
3.WORKING
4.APPLICATION
7

24.
INTRODUCTION
❑ Carbon- Dioxide (CO2) LASER was one of the earliest Gas lasers invented by
Kumar Patel of Bell Labs in 1964,is one of the most useful.
❑ CO2 gas lasers are the highest- power continuous wave lasers that are
currently available. They are also Quite efficient; the ratio of output power to
pump power can be large as 20%.
❑ The CO2 lasers produces a beam of infrared light with principal wavelength
bans centering around 9.6 and 10.6 micrometers.
8

25.
CONSTRUCTION OF CO2 LASER
➢ It consists of discharge tube size about 2.5 cm in diameter and 5 cm in
length. Two optically plane and parallel mirrors.
➢ The discharge tube is filled with a mixture of CO2, nitrogen and Helium
gases in the ratio of 15% 15% 70% respectively at a pressure of few mm of
Mercury.
➢ High value of DC voltage is used for electrical discharge in the tube due to
the co2 molecule break into CO and O and to maintain the equilibrium of
CO2 molecule, a small amount of water is added to regenerate the co2
molecule.
9

26.
Vibrational states in CO2 Molecule
10

27.
WORKING
11

28.
WORKING
 Vibrational and rotational modes of CO2 can not be excited themselves by
Photons.
 When a voltage is placed across the gas, electrons collide with the N2
molecules and excite them to their lowest vibrational levels.
 These vibrational levels happen to be at an energy very close to the energy
of the asymmetric vibrational states in the co2 molecule. Now, the excited
N2 molecules populate the asymmetric vibrational states in the CO2
molecule through Collisions.
12

29.
13

30.
APPLICATION
 Because of the high power CO2 lasers are frequently used in industrial
application for cutting and welding.
 They are also very useful in surgical procedures because water absorbs this
frequency of light very well.
 Some examples of medical uses are Laser surgery, Skin resurfacing ( Laser
Facelifts).
14
BEFORE AFTER

31.
ADVANTAGES
 In CO2 The CO2 laser offers the lowest cost per watt along with
good beam quality, The high power levels are obtained ranges from
few watts to 15000 watts.
 The efficiency of CO2 gas lasers (i.e. 10% or higher) is beat than He-
Ne and argon lasers.
 Long sealed-off lifetime of greater than 20,000 hours.
 Small size per watt of output power.
15

32.
DISADVANTAGE
 Divergence of CO2 lasers approximately in all cases is greater than
He-Ne and Argon laser. Usually the divergence is ranges from 1 to
10 milli radians.
 Beam width varies from 3mm to 100mm.
 Some CO2 lasers have the disadvantage of a short and thick optical
cavity.
 Its cost is comparatively high.
16

33.
ARGON (Ar) Laser :-

34.
What is an Argon Gas Laser?
❖ William Bridges, Professor of Electrical Engineering and Applied
Physics, California University invented the Argon gas laser in 1964.
❖ The Argon laser is a laser system that uses noble gas as the Active
Medium.
❖ The Argon ion Laser oscillates simultaneously on two transitions
having wavelength 4881Å (blue) and 5145 Å (green).
❖ This device emits wavelengths of blue/green colour
monochromatic light source and each wavelength has a very
narrow bandwidth.

35.
Construction of Argon Laser :-

36.
Construction of Argon Laser :-
❑ An Argon Ion laser is a gas laser in which ionized Argon gas is
used as the active or lasing medium.
❑ The Argon ion Laser consists of a long - narrow discharge tube
made of BeO filled with Ar gas having two Windows at its ends
inclined at Brewster’s angle.
❑ The narrow discharge tube act as an optical resonator or cavity as
two Mirrors are placed at each end of the tube facing
perpendicular to the length of the tube.
❑ When a high voltage is applied between the cathode and anode, a
high current flows.

37.
Energy Level Diagram :-

38.
Working Of Argon Laser :-
❑ In the first step, neutral Argon atoms are ionized and raised to energy
level E1 (known as the ground state of argon ions).
❑ In the second step, on the ion in the ground state are excited to energy
level E3.
❑ The excited Argon ion in energy labels E3 falls back to energy level E2
either the spontaneous emission or by stimulated emission process.
❑ The ions in energy level E2 decay spontaneously to the ground state of
argon-ion emitting a photon of wavelength 720Å ( ultraviolet Photon).
❑ Argon laser generates up to 18 discrete lines (wavelength) ranging from
ultraviolet (720 Å) to visible green (5145Å).

39.
Advantages of Argon laser :-
1. The width of the spectrum of Argon ion laser is large i.e. it
emits multiple wavelengths.
2. The output of the Argon laser is high as compared to the
output of the He-Ne laser.
3. Argon laser is a high gain system.
4. Divergence of the Argon laser
is very small.

40.
Wavelength Scenario :-

41.
Disadvantages of Argon Laser :-
1. The cost of an Argon laser is more than that of a He-Ne laser.
2. Construction of Set-up is difficult.
3. The efficiency of the argon laser
is very small.
4. Large amount of power supply
is needed to operate Argon laser.

42.
Applications of Argon laser :-
1. Argon lasers are used to treat
glaucoma and diabetic eye diseases.
2. Used in Raman spectroscopy.
3. Used in holography.
4. Used in forensic science.
5. Used as sources for optical pumping.
6. Laser shows in entertainment

43.
Differences among lasers Based on Classe
:-
LASER
Wavelength
Based
Media
Based
Sensitivity
Based
Industrial
Uses
Based
Appl.
Based

44.
Wavelength Based Differences
among lasers :-

45.
Sensitivity Based
Differences
among lasers :-

46.
Sensitivity Based Differences among lasers :-

47.
Industrial Uses Based Differences
among lasers :-