CHAPTER 6 PRINCIPLES OF LASERS

TM 9-258

CHAPTER 6

PRINCIPLES OF LASERS

from the partially mirrored end of the tube.

6-1.

General.

Simply defined, a laser (Light

(4) Liquid-type lasers consist of solutions

Amplification by Stimulated Emission of Radiation) is a

such as coumarine and rhodamine red. In this type of

light-emitting body with feedback for amplifying the

laser, the liquid-laser materials are stimulated to

emitted light.

The laser is a unique, and highly

emission by irradiating the lasing liquid or dye solution

specialized source of light; the beam of light it produces

with another laser beam.

has three significant characteristics, namely, laser light is

b. Although the heart of a laser is a light wave

monochromatic, highly collimated, and coherent.

amplifier, the device produces a beam when it oscillates.

Although light possessing the first two properties can be

The laser is, therefore, a special kind of oscillator, but it

produced by some conventional light sources, only laser

will optically behave in the same manner as ordinary

light possesses all three properties. In addition, the laser

light. For this reason, only gas lasers and solid-state

beam is a powerful and very intense light source.

rod-type lasers, are described in detail.

6-2.

Types of Lasers.

6-3.

Gas Lasers.

a. There are essentially four types of lasers:

a. A gas laser is structurally a simple device,

(1) Solid state rod-type lasers use

and in many ways it is similar to neon electric signs. A

materials such as a ruby rod of about 1 centimeter in

gas laser (fig 6-1) consists of a thin glass tube about 1

diameter and 15 centimeters long as an elementary light

foot long, and filled with a low-pressure mixture of helium

emitter or generator.

and neon gases. A pair of electrodes, a negative

(2) Semiconductor

diode-type

lasers

cathode and a positive anode, are mounted near the

use material such as gallium arsenide and consist of a

ends of the tube. These electrodes are connected to a

junction formed by p-type material and an n-type

high voltage, direct current power supply. The electric

material. In this type of laser, stimulation to laser

field produced between the two electrodes breaks down

emission occurs by passing a current through the

the column of gas, instantly transforming it from a poor

junction.

conductor of electricity into a relatively good conductor.

(3) Gas-type lasers use helium-neon,

A continuous electric glow discharge takes place within

argon, carbon dioxide, nitrogen and Xenon. In this type

the glass tube, and produces a continuous electric

of laser, stimulation to laser emission occurs by passing

current flow between cathode and anode through the

a current through the gas. The current causes the gas to

partially ionized column of gas.

ionize and radiate. The radiation oscillates within a tube

provided with mirrored ends and then discharges

Figure 6-1. Gas laser.

6-1