A PRESENTATION ON LASER
BY:-
NAME- Phonindra Madhav Gogoi
Roll No.- 10 (Bsc 4th sem Dept. of Physics)
Debraj Roy College
Contents
Introduction of laser
Principle of laser
Construction and working of laser
Types of laser
Construction and working of Ruby laser
Applications of laser
Introduction
The word ‘LASER’ is an acronym for ‘Light Amplification by Stimulated
Emission of Radiation’.
Laser is a device that emits a collimated , highly intense unidirectional
beam of light . Laser differ from other sources of light because they emit
light coherently, allowing the light to be focused to a tight spot.
Properties of laser light
1.The laser light is highly monochromatic.
2.The laser light is highly coherent.
3.The laser beam is extremely intense.
4.The laser beam is highly directional.
Principle of laser
The principle of laser is based on three separate features :
1. Stimulated emission within an amplifying medium.
2. Population inversion and optical pumping.
3. Optical resonator.
It involves exciting atoms within an active medium to higher energy levels
using an external energy source. When these excited particles return to
their lower energy state , they emit photons. For stimulated emission of
radiation to take place , the population of atoms in higher energy level should
be greater than the lower energy level. This can be achieved by photon
multiplication within an optical resonator cavity.
Stimulated Absorption, Spontaneous Emission and Stimulated Emission
According to Einstein, the interaction of radiation with matter could be
explained in terms of three basic processes.
1. Stimulated Absorption
It is a process where an atom absorbs a photon
of a specific frequency, causing it to transition
from a lower energy state to a higher energy
state.
2. Spontaneous Emission
It is the process in which an atom transit from
an excited energy state to a lower energy state
( i.e ground state) and emits a quantized amount
of energy in form of photon, without any
external agency.
3. Stimulated Emission
It is a process where an atom in an excited state is prompted to release a
photon in the presence of another photon with the same energy, phase &
direction, leading to the emission of coherent light.
* Metastable states
Metastable state can be defined as a state where excited atoms can remain
for longer time than in the normal excited state.
Atoms excited to the metastable state have an
appreciable lifetime( ~10-6 to 10-3 sec) which is
103 to 106 times the life times of the ordinary
energy state.
Population Inversion & Pumping
Population inversion is the condition where, in a collection of atoms, the
number of particles in an excited energy state is greater than the number
of particles in a lower energy state. It is essential for operation of laser, as
it allows for the amplification of light or microwave radiation through
stimulated emission.
The process by which population inversion is achieved is called Pumping.
It involves supplying energy to a system to excite particles from lower energy
state to a higher energy state. The commonly used methods for pumping are:
optical pumping, electrical discharge , chemical reaction, etc.
In optical pumping, high energy light
source such as xenon flash lamp is
used to excite the electron.
Construction and working of Laser
There are three main components of LASER namely-
1. Active or gain medium.
2. Pumping source.
3. Optical resonator.
A laser is constructed with a gain medium, energized by a pump to elevate
electrons, and an optical resonator made of two mirrors to amplify the
emitted photons when these electrons fall back to lower energy state
One partially reflective mirror allows the amplified light to escape as a
coherent laser beam.
This setup produces
a focused beam of
light of a specific wav-
-elength, depending
on the gain medium.
* Working-
Laser work through the principles of light amplification and stimulated emission.
The working of laser, involves a process that amplifies light to produce a highly
focused, coherent beam of photons.
- The first step in the operation of laser is the pumping of energy into the gain medium
- Due to pumping the atoms in gain medium excite to higher energy state creating a
population inversion.
- Atoms in excited state returns to lower energy state with release of photons i.e
spontaneous emission takes place.
- When a photon of specific energy encounters another atom in excited state, it stimulate
the atom to emit a second photon of same energy, phase & direction as the first. Each
photon can stimulate the emission of further photon, leading to chain reaction.
- The gain medium is placed between two mirrors(one is fully& other is partially reflective)
forming an optical resonator.The photons produced bounce back & forth between the
mirror, stimulating more emissions as the passes through the gain medium, thus amplify-
-ing the light..
- The light that is aligned with the axis of mirror is amplified and eventually emerges from
the partially reflective mirror as laser beam.
Types of Laser
A. Based on the laser levels, lasers are of two types-
1. Three level laser-
A three level laser system is one of the simplest
forms of laser design, characterized by its use of
three distinct energy state(level) in the lasing
process. Example- Ruby laser.
2. Four level laser-
A four level laser system adds an extra energy state
into the operation of laser, creating a more efficient
process than the three level laser system. This system
is characterized by having four distinct energy state
involved in the lasing action.
Example- He-Ne laser.
B. Based on the active medium used there are mainly five types of laser
1. Solid state laser-
It utilize a solid material as the gain medium, typically doped with ions that
provides the energy states necessary for laser operation.
2. Gas laser-
It use a gas or a mixture of gases as the active medium.
3. Semiconductor or Diode laser-
It use semiconductor medium as the gain medium.
4. Liquid or Dye laser-
It use an organic dye as the gain medium.
5. Fiber laser-
It use a doped optical fiber as the gain medium. They are known for their high
output power, excellent beam quality and efficiency.
Ruby Laser
The Ruby laser was first working laser developed in 1960 by
Theodore Maiman. It belongs to the class of solid state laser.
The main characteristics of Ruby laser are-
1. It is a solid state laser. Theodore H Maiman
2. It is a three level laser.
3. It works in pulse mode.
* Construction-
* Working-
Ruby is Al2O3 doped with Cr3+ ions which are responsible for lasing. The Cr3+ ions
have their energy levels as in the figure, which is basically a three level system.
When Xenon flash lamp is switched on, the 5500 A radiation photon excites Cr3+
ions to E3 excited state. As E3 is highly unstable, so Cr3+ ions undergo non radia-
-tive transition to the state E2 which is the metastable state. When more than half
of Cr3+ ion population accumulates at E2, the population inversion established
between E2 & E1 due to pumping the no. of Cr3+ ions in E1 goes on decreasing. A
photon emitted spontaneously due to transition of Cr3+ ion in E2 initiate stimulat-
ed emission by other Cr3+ ions in the metastable state. The photons of wavelength
6943A emitted due to stimulated emission travel along axial direction of Ruby rod
and are repeatedly reflected back & forth by the silvered ends and & finally emerge
out of the partially silvered end as a strong beam of laser with red color.
Applications of Laser
Laser light is different from ordinary light & because of its unique properties it
is used in various applications.
The most significant applications of laser include:
1. Laser in medical field-
a. It is used for eye surgery, cosmetic treatment.
b. It is used cancer diagnosis. Etc
2. Laser in communication-
a. It is used in space communication, radars,
satellites & in underwater communications.
b. It is used in optical fiber communications, etc.
3. Laser in Industries-
a. Lasers are used to cut glass & quartz.
b. Lasers are used in semiconductor industries
for photolithography, etc.
4. Laser in Science and Technology-
a. Lasers are used in computer printer and in
various devices.
b. Lasers are used to retrieve stored information from CD.etc
5. Laser in Military-
a. Laser as a range finder, tracker & as a weapon.
b. Used for jamming or destruction of sensors, etc.
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