CHAPTER 2
INTRODUCTION TO LASERS
The word laser is an acronym for Light
Amplification by Stimulated Emission of Radiation.
The first lasers were used for surveying applications,
as they gave an accurate measurement of distance. As
the technology increased, laser systems were adapted
for military applications. The initial application was
for gunfire control.
Today, lasers are used in the
military for range finding, target designation, com-
munications, target detection, and landing systems,
and training aids. In the civilian community, lasers
are used in the medical field and for welding, cutting,
surveying, and communications.
CHARACTERISTICS OF A LASER
A simplified illustration of a typical solid-state
laser is shown in figure 2-1. The elements of the laser
are:
. Lasing material (crystal, gas, etc.)
. Pump source (flash lamp, electron collision,
etc.)
l Optical cavity
. Laser radiation
Lasers operate on the principle of stimulated
emission. Electrons in the atoms of the lasing material
reside in a steady-state. When energy is added to an
atom, an unstable condition occurs when its electrons
are excited to a higher energy level. The electrons
will stay in this state for a short time and then decay
back to their original energy state. This decay occurs
in two ways:
1.
2.
Spontaneous decay—the electrons simply fall
to their ground state while emitting randomly
directed photons; and
Stimulated decay—the photons from
spontaneous decaying electrons strike other
excited electrons, which causes them to fall to
their ground state.
This transition through stimulated decay will
release energy in the form of photons of light that
travel in phase and in the same direction as the
incident photon.
If the direction is parallel to the
optical axis, the emitted photons will travel back and
forth in the optical cavity, through the lasing material,
between the 100-percent reflecting mirror and the
99-percent reflecting mirror. The light energy is
amplified each time the beam passes through the
lasing material. When sufficient energy is built up in
the beam, a burst of light will be transmitted through
the 99-percent reflecting mirror. This action is called
lasing.
Figure 2-1.—Typical solid-state laser configuration.
2-1
