The document discusses the history, components, and applications of lasers, focusing on various types such as the Nd:YAG and CO2 lasers. It highlights the theoretical foundations given by Einstein and early practical demonstrations, detailing the mechanisms of operation, energy levels, and output characteristics. Applications include industrial materials processing, medical procedures, and military uses.

1. LASER
( Light Amplification by Stimulated Emission Radiation )
Aman 28-10-2014 Dhanda ( Aerospace Engg. ) 1

2. Introduction
The first theoretical foundation of LASER and MASER was given by Einstein in 1917
using Plank’s law of radiation that was based on probability coefficients (Einstein
coefficients) for absorption and spontaneous and stimulated emission of electromagnetic
radiation. Theodore Maiman was the first to demonstrate the earliest practical laser in 1960
after the reports by several scientists, including the first theoretical description of R.W.
Ladenburg on stimulated emission and negative absorption in 1928 and its experimental
demonstration by W.C. Lamb and R.C. Rutherford in 1947 and the proposal of Alfred Kastler
on optical pumping in 1950 and its demonstration by Brossel, Kastler, and Winter two years
later. Maiman’s first laser was based on optical pumping of synthetic ruby crystal using a
flash lamp that generated pulsed red laser radiation at 694 nm. Iranian scientists Javan and
Bennett made the first gas laser using a mixture of He and Ne gases in the ratio of 1 : 10 in
the 1960. R. N. Hall demonstrated the first diode laser made of gallium arsenide (GaAs) in
1962, which emitted radiation at 850 nm, and later in the same year Nick Holonyak
developed the first semiconductor visible-light-emitting laser.
Aman 28-10-2014 Dhanda ( Aerospace Engg. ) 2

3. LASER COMPONENTS
 ACTIVE MEDIUM
Solid (Crystal)
Gas
Semiconductor (Diode)
Liquid (Dye)
 EXCITATION MECHANISM
Optical
Electrical
Chemical
 OPTICAL RESONATOR
HR Mirror and
Output Coupler
• The Active Medium contains atoms which can emit light by
stimulated emission.
• The Excitation Mechanism is a source of energy to excite the
atoms to the proper energy state.
• The Optical Resonator reflects the laser beam through the active
medium for amplification.
28-10-2014 Aman Dhanda ( Aerospace Engg. ) 3

4. Nd (Neodymium) – YAG (Yttrium Aluminium
Garnet) LASER
Principle :
Doped Insulator laser refers to yttrium aluminium garnet doped with
neodymium. The Nd ion has many energy levels and due to optical
pumping these ions are raised to excited levels. During the transition
from the metastable state to E1, the laser beam of wavelength
1.064μm is emitted.
Type  : Doped Insulator Laser
Active Medium  : Yttrium Aluminium Garnet
Active Centre  : Neodymium
Pumping Method  : Optical Pumping (Xenon Flash Pump)
Optical Resonator  : Ends of rods silver coated
Two mirrors partially and totally reflecting
Power Output  : 20 Kilowatts
Nature of Output  : Pulsed
Wavelength Emitted  : 1.064 μm
Characteristics :
Aman 28-10-2014 Dhanda ( Aerospace Engg. ) 4

5. Nd : YAG LASER Diagram
Non radioactive decay
Laser
1.064μm
Non radioactive decay
E3
E2
E
4
E1
E0
Nd
Energy Level Diagram of Nd : YAG laser
E1, E2, E3 – Energy levels of Nd
E4 – Meta Stable State
E0 – ground State Energy Level
Aman 28-10-2014 Dhanda ( Aerospace Engg. ) 5

6. Application of Nd : YAG Laser
 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.
Aman 28-10-2014 Dhanda ( Aerospace Engg. ) 6

7. CO2 ( Carbon dioxide ) LASER
Principle :
The transition between the rotational and vibrational energy levels lends
to the construction of a molecular gas laser. Nitrogen atoms are raised
to the excited state which in turn deliver energy to the CO2 atoms
whose energy levels are close to it. Transition takes place between the
energy levels of CO2 atoms and the laser beam is emitted.
Type  :Molecular gas laser
Active Medium  :Mixture of CO2, N2, He or H2O vapour
Active Centre  : CO2
Pumping Method  : Electric Discharge Method
Optical Resonator  : Gold mirror or Si mirror coated with Al
Power Output  : 10 kW
Nature of Output  : Continuous or pulsed
Wavelength Emitted  : 9.6 μm or 10.6 μm
Characteristics :
Aman 28-10-2014 Dhanda ( Aerospace Engg. ) 7

8. 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. Modes of vibration in CO2
Symmetric C - stationary
O - vibrates simultaneously
along molecular axis
Bending C & O vibrate perpendicular to
molecular axis
Asymmetric Stretching C & O atoms vibrate in
opposite directions along
molecular axis
Aman 28-10-2014 Dhanda ( Aerospace Engg. ) 8

9.  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.
Diagram
 This energy level corresponds to one of the vibrational
- rotational level of CO2 molecules, designated as level
4.
 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.
Energy Level Diagram of CO2
Aman 28-10-2014 Dhanda ( Aerospace Engg. ) 9

10.  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.
 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.
Aman 28-10-2014 Dhanda ( Aerospace Engg. ) 10

11. Application of CO2 Laser
• Because of the high power levels available (combined with reasonable cost for the laser),
CO2 lasers are frequently used in industrial applications for cutting and welding, while lower
power level lasers are used for engraving.
• They are also very useful in surgical procedures because water (which makes up
most biological tissue) absorbs this frequency of light very well. Some examples of medical
uses are laser surgery and skin resurfacing ("laser facelifts", which essentially consist of
vaporizing the skin to promote collagen formation). Also, it could be used to treat certain skin
conditions such as hirsuties papillaris genitalis by removing embarrassing or annoying bumps,
podules, etc. Researchers in Israel are experimenting with using CO2 lasers to weld human
tissue, as an alternative to traditional sutures.
• The common plastic poly (methyl methacrylate) (PMMA) absorbs IR light in the 2.8–25 μm
wavelength band, so CO2 lasers have been used in recent years for fabricating microfluidic
devices from it, with channel widths of a few hundred micrometers.
• Because the atmosphere is quite transparent to infrared light, CO2 lasers are also used for
military rangefinding using LIDAR techniques.
• CO2 lasers are used in the Silex process to enrich uranium.
28-10-2014 Aman Dhanda ( Aerospace Engg. ) 11
• The Soviet Polyus was designed to use a megawatt carbon-dioxide laser as an orbit to orbit

12. 28-10-2014 Aman Dhanda ( Aerospace Engg. ) 12