Lasers 2

We have all at some point in our lives used or seen someone

use a laser. They are used in compact disc players for stereos or

computers, laser surgery, laser printers, holography, cutting and

borring metals, communication, bar-code scanners, etc. Over the past

three decades' lasers have become a tool used daily by many people

and they have become very useful in scientific research. As you can

see lasers are a very useful and important tool which is why I have

chosen this topic to write about.



The term laser is an acronym. It stands for "light amplification by

stimulated emission of radiation". They produce a narrow, intense

beam of coherent light.



In a laser the atoms or molecules of a crystal, like ruby or

garnet-or of a gas, liquid, or other substance-are excited so that more

of them are at higher energy levels than are at lower energy levels. If a

photon whose frequency corresponds to the energy difference

between the excited and ground states strikes an excited atom, the





atom is stimulated, as it falls back to a lower energy state, to emit a

second photon of the same frequency, in phase with and in the same

direction as the bombarding photon. This process is called stimulated

emission. The bombarding photon of the emitted photon may then

strike other excited atoms, stimulating further emission of photons, all

of the same frequency and phase. This process produces a sudden

burst of coherent radiation as all the atoms discharge in a rapid chain

reaction. The light beam produces is usually pencil thin and maintains

its size and direction over very long distances.



Lasers vary greatly in the way they look and what they are used

for. Some lasers are as large as buildings while others can be the size

of a grain of salt.



There are many parts to lasers. I will now explain what they are

and their uses.



1) Pumping systems:

The pumping system is used to transmit energy to the atoms or



molecules of the medium used in the laser.

a. optical pumping systems uses photons provided by a source such

as a Xenon gas flash lamp or another laser to transfer energy to the

lasing material. The optical source must provide photons which

correspond to the allowed transition levels of the lasing material.

b. collision pumping relies on the transfer of energy to the lasing

material by collision with the atoms or molecules of the lasing

material. Again, energies which correspond to the allowed transition

must be provided. This often done by electrical discharge in a pure

gas - or gas mixture - in a tube.

c. chemical pumping systems use the binding energy released in

chemical reactions to raise the lasing material to the metastable

state.



2) Optical Cavity:

An optical cavity is required to provide the amplification desired in

the laser and to select the photons which are traveling in the desired

direction. As the first atom or molecule in the metastable state of the




inverted population decays it triggers (by stimulated emission) the

decay of another atom or molecule in the metastable state.



3) Laser Media:

Lasers are usually classified by the lasing material used by the

laser. There are four types which are solid state, dye, gas and

semiconductor.

a. solid state lasers employ a lasing material distributed in a soloid

matrix sytem. Accessory devices which may be internal or external

may be used to convert the output .


b. gas lasers use a gas or a mixture of gas within a tube. The most

common gas laser uses a mixture of helium and neon with a pimary

output of 632.8 nm which is a red visible colour.

c. dye lasers use a laser medium that is ususally a complex organic

dye in a liquid solution or suspension. The most striking feature of

these lasers is their "tunability". Proper choice of the dye and it's

concentration allows production of laser light over a broad range of

wavelength in or near the visible spectrum.

d. semiconductor lasers are not to be confused with solid state lasers.

Semiconductor devices consist of two layers of semiconductor

material sandwiched together.



Laser Applications

Laser Surgery

The small, intense, bright beam of light can be focused with lenses to

provide a point of energy intense enough to burn through living flesh.

Laser Welding, Cutting & Blasting

Once again the laser's intense energy when focused make it ideal for

providing concentrated welding and cutting.

Laser Shows

The intense color of laser light has opened up a whole new world for

laser artists to weave a new kind of art using different coloured lenses,

mirrors and crystals.

Power Generation

Laser-powered fusion holds hope of generating tremendous amounts

of electricity through the use of lasers.


Information Technology

Using fiber optic bundles to carry them, modulated laser beams can

transfer huge amounts of information(internet). Lasers in compact disc

players read tiny reflections on CD's and laser discs to play back

audio and video. Someday your house could be fitted with fiber optics

to carry cable tv and phone service.