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Laser |
An acronym for
light
amplification by
stimulated
emission of radiation.
A laser is a cavity, with mirrors at the ends, filled with material
such as crystal, glass, liquid, gas or dye. A device which produces
an intense beam of light with the unique properties of coherence,
collimation and monochrome.
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Laser Components |
Lasers
contain four primary components, there are active medium, excitation
mechanism, high reflectance mirror and partially transmissive
mirror.
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The distance between
diametrically opposed points in the cross section of a circular
beam where the intensity is reduced by a factor of 1/e (0.368)
of the peak level (for safety standards). The value is normally
chosen at 1/e2 (0.135) of the peak level for manufacturing
specifications.
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Angle of beam spread
measured in radians or milliradians. For small angles where the
cord is approximately equal to the arc, the beam divergence can
be closely approximated by the ratio of the cord length (beam
diameter) divided by the distance (range) from the laser
aperture.
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A term used to describe
how the power of a laser beam is geometrically distributed
across the cross section of the beam. Also used to describe the
operating mode of a laser such as continuous or pulsed.
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The
different time modes of operation of a laser are continuous wave
(CW) lasers, single pulsed lasers, single pulsed Q-switched
lasers, repetitively pulsed lasers and mode-locked lasers.
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The number of light
waves passing a fixed point in a given unit of time, or the
number of complete vibrations in that period of time.
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Longitudinal Modes |
These
"longitudinal modes" result from the boundary conditions that, in a
conventional two-mirror lasers, the amplitude of the wave must be
zero at the mirror surface (i.e., that the oscillating wave is a
standing wave). This means only those laser frequencies that meet
the criterian = nc/2L can operate, where c is the speed of light, L
is the effective cavity length, and n is an interger. Adjacent modes
are typically orthogonally polarized.
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Transverse Modes |
Transverse modes have a
field vector normal to the direction of propogation and are
determined by the geometry of the laser or waveguide cavity and any
limiting apertures. The lowest order mode is the Gaussian TEM00.
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TH |
A thermistor
is a temperature measuring device which is typically used in a
feedback loop to stabilize the temperature of the laser. |
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FAC |
A
Fast axis
colimator (FAC) is a cylindircal lens
mounted directly to the laser submount which decreases the fast axis
of the laser emission from 40 degrees to approximately 2 degrees.
Coupling loss through a FAC is typically 5%.
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Thermoelectric
coolers (TEC's) are electronic devices
which can either cool or heat a device when current is applied. They
are typically used in conjunction with a thermistor to stabilize the
temperature of a laser.
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Apparent Brightness |
The human eye can see light in the visible spectrum ranging
from Red to Violet, The eye's sensitivity is non linear, so
different colors are perceived at different intensities to
the eye. The color the human eye is most sensitive to is a
shade of Green which has a wavelength of 555nm.
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A measurement of laser
quality.
M2 has been defined to describe the deviation of the
laser beam from a theoretical Gaussian. For a theoretical
Gaussian, M2=1; for a real laser beam, M2>1.
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The ability to
superimpose an external signal on the output beam of the laser
as a control.
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The energy per second
measured in watts emitted from the laser in the form of coherent
light.
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Restriction of the
vibrations of the electromagnetic field to a single plane,
rather than the innumerable planes rotating about the vector
axis. Various forms of polarization include random, linear,
vertical, horizontal, elliptical, and circular.
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A protective housing is
a device designed to prevent access to radiant power or energy.
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The ability of a laser
system to resist changes in its operating characteristics.
Temperature, electrical, dimensional, and power stability are
included.
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The length of the light
wave, usually measured from crest to crest, which determines its
color. Common units of measurement are the micrometer (micron),
the nanometer, and (earlier) the Angstrom unit.
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