Figure 6-2. Solid-state rod lasers.

TM 9-258

b. The tube emits a reddish-orange neon glow

back and forth along the gas column establishing a

continuous lasing action.

because the electric discharge causes countless

d. The electric discharge continuously pumps

collisions among the gas atoms that excite them to high

the neon gas atoms to higher energy states, and, at the

energy states; the atoms randomly fall back to their

same time, light waves bouncing between the mirrors

normal energy state, and, in so doing, emit a bundle of

stimulate the excited atoms into emitting their packets of

light energy photons. In a conventional neon sign, these

light energy. As a result, a steady stream of coherent,

up and down energy shifts take place at random within

monochromatic light is generated within the column. The

the glowing gas column.

c. The mixture of gases in the laser tube has

laser tube's front mirror is designed to be partially

transmitting, i.e., it is designed to reflect 99% of the light

been carefully selected so that more neon atoms are in

that hits it, and allow the other 1% to pass through. This

high energy states than in low energy states when the

small portion of the laser light generated within the tube

discharge occurs; it is the neon gas that is responsible

passes through the front mirror as a narrow light beam;

for lasing. That is, as the discharge excites the helium

its wavelength is 633 nm, and it is deep red in color.

atoms, they collide with the neon atoms and transfer

energy to the neon atoms. This transfer of energy to the

6-4.

Solid State Rod Lasers.

neon atoms raises their energy state.

Stimulated

a. A ruby rod solid state laser consists of an

emission of photons can now take place within the

elementary light emmitter or generator that is illuminated

column of glowing gas. This occurs when an excited

by a high-intensity light (A, fig 6-2). The high-intensity

neon atom drops to a lower energy level and emits a light

light, such as that from a photoflash lamp, makes the rod

wave. As the light wave speeds past other excited

fluoresce with a pink color. The fluorescence persists as

atoms, it stimulates them to emit their photons. This

long as the photoflash light persists. This effect is not a

process of amplification continues, since one photon

laser radiation, but just another optical characteristic of

entering the column of gas at one end causes other

the emitter. The ruby rod produces a characteristic pink

photons to be emitted. The reflecting mirrors at the front

color because it is made of aluminum oxide (sapphire)

and the rear of the glass tube cause any light waves

containing 0.05 % chromium.

emitted in the direction of the tube to bounce

Figure 6-2. Solid-state rod lasers.

6-2