ACTIVE LEARNING ASSIGHMENT ON

TYPES OF LASER AND ITS APPLICATIONS

PRESENTED BY FACULTY

BHARGAV DESAI – 035 PRUTHVI GABANI -PARTH CHOVATIA-

BATCH A2

DEPERTMENT- CE

GANDHINAGAR INSTITUTE OF TECHNOLOGY

LASER

LASER

ight

mplification by

timulated

mission of

adiation

TYPES OF LASERS

•Solid State Lasers•Gaseous state Lasers•Dye Lasers•Semiconductors Lasers

Main Working of Lasers

A Laser covers mainly below given points:

Population Inversion Pumping Direct Conversion Lasing Life Time Metastable State Active Medium Optical Resonator

Different Types of Lasers

Solid State Lasers Gaseous state Lasers Ruby Lasers

Ne- He Laser

Semi conductors Lasers

Ga-As Laser

Active Medium:

•The active laser medium (laser gain/amplification medium) is a synthetic ruby rod.

•Ruby is an aluminum oxide crystal in which some of the aluminum atoms have been replaced with chromium atoms(0.05% by weight).

•Chromium gives ruby its characteristic red color and is responsible for the lasing behavior of the crystal.

•Chromium atoms absorb green and blue light and emit or reflect only red light. For a ruby laser, a crystal of ruby is formed into a cylinder.

Resonator Cavity : A resonator cavity is made of flash tube like solenoid with a ruby rod in the centre , both the side mirrors one partial reflecting mirror and other fully.

1. RUBY LASER

OPTICAL PUMPING:

A xenon lamp is rolled over ruby rod and is used for pumping ions to excited state.

RUBY LASER (WORKING)

WORKING:Ruby laser is based on three energy levels. The upper energy level E3 I short-lived, E1 is ground state, E2 is mate stable state with lifetime of 0.003 sec.

RUBY LASER ( WORKING ).

The ions after giving a part of their energy to crystal lattice decay to E2 state undergoing radiation less transition.

In meta stable state , the concentration of ions increases

while that of E1 decreases. Hence , population inversion is achieved.

Meta stable state

Application

Ruby lasers have declined in use with the discovery of better lasing media. They are still used in a number of applications where short pulses of red light are required. Holography around the world produce holographic portraits with ruby lasers, in sizes up to a meter squared.

Many non-destructive testing labs use ruby lasers to create holograms of large objects such as aircraft tires to look for weaknesses in the lining.

Ruby lasers were used extensively in tattoo and hair removal

ACTIVE MEDIUM:

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.

PUMPING:

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.

OPTICAL PUMPING:

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.

2.He-Ne Laser ( Helium Neon)

CONSTRUCTION:

Here helium and neon gas in appropriate amount is taken in the glass type of cavity, here on both opening there are mirrors ,one of fully reflecting and other partially. Inside the cavity one end is connected with the cathode and other with the anode,futherConnected with the AC supply.

He-Ne Laser (construction).

WORKING:

•When the power is switched on, An energetic electron collision excites a He atom to the stable state.

• The excited He*(21 S) atom collides with an unexcited Ne atom and the atoms exchange its internal energy, with an unexcited Ne atom and excited He atom. 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.

•When the excited Ne atom passes from meta stable state(3s) to lower level(2p), it emits photon of wavelength 632 nm.

He-Ne LASER ( Working ).

•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 non radioactive

•transition.

He-Ne LASER ( WORKING ).

Application:

•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.

He-Ne Laser (Application).

3. SEMI CONDUCTOR LASER

INTREODUCTION:

Stimulated, organized photon emission occurs when two electrons with the same energy and phase meet. The two photons leave with the same frequency and direction.

In 1916 Einstein devised an improved fundamental statistical theory of heat, embracing the quantum of energy. His theory predicted that as light passed through a substance it could stimulate the emission of more light. This effect is at the heart of the modern laser.

Mainly there are two types in semiconductor laser:

(1)Homo junction laser

(2)Hetero junction laser

PUMPING:

When PN junction diode is forward biased, the electrons from ‘n’ region and holes from ‘p’ region recombine with each other at the junction .

During the recombination process light radiations (photons) is released from certain specified direct band gap semiconductors like Ga-As.

This radiation is called recombination radiation and the corresponding energy is called activation energy.

Ga-As LASER

METALLIC LAYER

Ga As CONTACT LAYER

Ga Al As BARRIER LAYER

Ga As CONTACT LAYER LASERBEAM

Ga Al As BARRIER LAYER

Ga As CONTACT LAYER

+ -

GALLIUM ARSENIDE LASER

Ga- As Laser Construction

WORKING:

When the forward bias is applied to the metallic layer through contact points. The electric field is produced. This electric field causes the electrons to move from lower band of energy towards high band of energy level.

Population inversion take place at the higher band of energy level and when the electrons falls back at the lower energy band, it emits light, through the polished end of the laser.

Cross reflection of the light take place which multiplies strength of laser beam. At the end strong beam of laser comes out through the partially polished end.

Ga-As LASER

Advantages of semiconductor laser

It is very small in dimension.

The arrangement is simple and compact.

It exhibits high efficiency.

Disadvantages of semiconductor laser

The output is usually in the form of wide beam.

The purity & mono chromaticity are poorer than

other type of laser.

Applications:

Semiconductor diode lasers used in CD

and DVD players.

Fiber optic transceivers are manufactured using

alternating layers of various III-V and II-

VI compound semiconductors to form lasing hetero

structures.

Used in laser printers & in laser diodes.

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