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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 monochromaticity.
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Laser
Accessories
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The
hardware and options available for lasers, such as secondary
gases, Brewster windows, Q-switches, and electronic shutters.
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Laser
Damage Threshold |
The resistance of an optical component to laser induced damage
is quantified in an irradiation power density expression know
as laser damage threshold. The most common laser damage process
this is often initiated at a dielectric surface or interface
by the ionization of a contaminant molecule such as water
that has been absorbed on a surface or trapped at an interface.
Ionization can also occur in the interior of a pure dielectric,
where the very high photon fluxes of some pulsed lasers may
induce a process known as multi-photon ionization.
A rare phenomenon
that results in acoustic amplification and subsequent mechanical
damage.
Energy absorption
at inclusions that leads to thermal fracture can occur, but
it is unusual in high-quality dielectric materials.
In addition to
these effects, polishing imperfections such as scratches and
digs can result in constructive interference of reflected
or diffracted waves in which the resultant electric fields
can potentially cause damage.
Laser damage threshold
is usually specified as a power per unit area for cw lasers
or as energy over time per unit area, for pulsed lasers. A
typical specification for a high-energy laser optic could
be 4.5 J/cm2
in 10 nsec at 355 nm.
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Laser
Oscillation |
The
buildup of the coherent wave between laser cavity end mirrors
producing standing waves.
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Laser
Rod
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A
solid-state, rod-shaped lasing medium in which ion excitation
is caused by a source of intense light, such as a flashlamp.
Various materials are used for the rod, the earliest of which
was synthetic ruby crystal.
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Laser
System |
An
assembly of electrical, mechanical, and optical components
which includes a laser. Under the Federal Standard, a laser
in combination with its power supply (energy source).
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Leading
Edge Spike |
The
initial pulse in a series of pulsed laser emissions, often
useful in starting a reaction at the target surface. The trailing
edge of the laser power is used to maintain the reaction after
the initial burst of energy.
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Lens |
A
curved piece of optically transparent material which depending
on its shape is used to either converge or diverge light.
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Lens
Maker's Formula |
The
standard formula for determining the focal length of a thin
lens (thickness = 0) with radii of curvature r1
and r2. The focal length is given by the equation
1/f = (n - 1)[(1/r1) - (1/r2)]
where
f is the focal length and n is the index of refraction of
the material.
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Light |
The
range of electromagnetic radiation frequencies detected by
the eye, or the wavelength range from about 400 to 760 nanometers.
The term is sometimes used loosely to include radiation beyond
visible limits.
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Limiting
Angular Subtense |
The
apparent visual angle which divides intrabeam viewing from
extended-source viewing.
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Limiting
Aperture |
The
maximum circular area over which radiance and radiant exposure
can be averaged when determining safety hazards.
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Limiting
Exposure Duration |
An
exposure duration which is specifically limited by the design
or intended use(s).
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Linear
Polarization |
With
respect to light radiation, the case where the polarization
direction is fixed.
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Longitudinal
or Axial Mode |
Determines
the wavelength bandwidth produced by a given laser system
controlled by the distance between the two mirrors of the
laser cavity. Individual longitudinal modes are produced by
standing waves within a laser cavity.
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