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TM 9-258
b.  In laser radiation, the ends of the ruby rod
photons, and these photons continue interacting to
produce still more photons. When a threshold energy of
are highly polished so that light can pass through almost
the total photonic energy within the resonant cavity is
without absorption. A mirror is placed at each end and
attained, a pulse, consisting of a very intense laser beam
aligned perpendicularly to the principal axis of the rod.
formed by photon waves, bursts out of the partially
When the rod is illuminated with an intense photoflash
reflective end of the ruby rod.
light, it emits a fluorescent light which reflects back and
e. In practical applications the highly polished ends of
forth between the two mirrors. This increase in intensity
the ruby rod can be mirrored or coated with a dielectric
of the light is produced by the oscillation of the ruby light
material, such as magnesium fluoride or cerium dioxide
within an optically resonant cavity formed by the rod and
(B, fig 6-2). When this is done one end is fully coated
the two reflecting surfaces of the mirrors.
c.  The removal of the laser energy, or
and the other is partially coated so that the emitted laser
light can pass through it. This laser beam, as it emerges
radiation, from the resonant cavity is accomplished by
from the ruby rod, has a slight divergence.
making the rear reflecting mirror 100% reflective and the
front reflecting mirror partially reflective.  This allows
6-5.
Laser Optics.
some of the laser light generated within the resonant
a.  The extremely tight beam produced by the
cavity to pass through as a laser beam of the same
laser, with final tightening obtained by external. optical
diameter as the ruby rod
systems, gives it the ability to travel extreme distances
d.  During the optical pumping of the ruby rod
with little divergence. The laser output can be focused to
by the flashlamp, some of the chromium in the ruby rod
a parallel beam where spreading is expected to be less
become excited. This causes their electrons to move
than one foot per mile of travel. A beam of light from a
away from the atoms and position themselves at higher
ruby laser would suffer so little divergence that, for
energy levels from which they spontaneously fall back to
example, it would be concentrated in an area ten miles
their normal energy states. During this transition, each
across when it reached the moon; an ordinary search
of these electrons produces a photon of light.  These
light with the same intensity would place a beam over
photons now oscillate by reflecting from one mirror
25,000 miles wide on the moon.
surface to the other within the resonant cavity. On their
b.  Brightness may approach millions of times
way to the mirror, some of the photons collide with one or
that of the sun, on a relative bandwidth basis. Spectral
more atoms which are in an excited state due to the
narrowness allows good signal to background ratios to
flashlamp pumping, and interact with them to produce a
be realized.  Compared to microwave systems, laser
photon or photons identical in energy and frequency with
devices will allow construction of equipment with an
the initial photon. The newly formed photons continue to
antenna only inches across.
interact with other excited atoms, producing more
6-3

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