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Radian
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A
unit of angular measure equal to the angle subtended at the
center of a circle by a chord whose length is equal to the
radius of the circle.
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Radiance
Brightness
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The
radiant power per unit solid angle and per unit area of a
radiating surface.
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Radiant
Energy (Q)
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Energy
in the form of electromagnetic waves usually expressed in
units of Joules (watt-seconds).
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Radiant
Exposure (H)
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The
total energy per unit area incident upon a given surface.
It is used to express exposure to pulsed laser radiation in
units of J/cm2.
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Radiant
Flux Radiant Power
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The
time rate of flow of radiant energy. Units-watts. (One [1]
watt = 1 Joule-per-second). The rate of emission of transmission
of radiant energy.
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Radiant
Intensity
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The
radiant power expressed per unit solid angle about the direction
of the light.
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Rayleigh
Scattering
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Scattering
of radiation in the course of its passage through a medium
containing particles, the sizes of which are small compared
with the wavelength of the radiation.
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Real
Image
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A
real image is one in which the light rays actually converge;
if a screen were placed at the point of focus, an image would
be formed on it.
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Reflection
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The
return of radiant energy (incident light) by a surface, with
no change in wavelength.
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Refraction
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The
change of direction of propagation of any wave, such as an
electromagnetic wave, when it passes from one medium to another
in which the wave velocity is different. The bending of incident
rays as they pass from one medium to another (e.g., air to
glass).
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Repetitively
Pulsed Laser
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A
laser with multiple pulses of radiant energy occurring in
sequence with a PRF > 1 Hz.
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Resonator
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The
mirrors (or reflectors) making up the laser cavity including
the laser rod or tube. The mirrors reflect light back and
forth to build up amplification.
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