BEAM A collection of rays that may be parallel, convergent, or divergent.
BEAM BENDER A hardware assembly containing an optical device, such as a mirror,
capable of changing the direction of a laser beam; used to repoint the beam, and
in "folded," compact laser systems.
BEAM DIAMETER The distance between diametrically opposed points in the cross
section of a circular beam where the intensity is reduced by a factor of e(-1)
(0.368) of the level (for safety standards). The value is normally chosen at e(-2)
(0.135) of the peak level for manufacturing specifications.
BEAM DIVERGENCE Angle of beam spread measured in radians more milliradians
(1 milliradian = 3.4 minutes-of-arc or approximately 1 mil). 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.
BEAM EXPANDER An optical device that increases beam diameter while decreasing
beam divergence (spread). In its simplest form consists of two lenses, the first
to diverge the beam and the second to re-collimate it. Also called an upcollimator.
BEAM SPLITTER An optical device using controlled reflection to produce two
beams from a single incident beam.
BLINK REFLEX See aversion response.
BREWSTER WINDOWS The transmissive end (or both ends) of the laser tube, made
of transparent optical material and set at Brewster's angle in gas lasers to achieve
zero reflective loss for one axis of plane polarized light. They are non-standard
on industrial lasers, but a must if polarization is desired.
BRIGHTNESS The visual sensation of the luminous intensity of a light source.
The brightness of a laser beam is most closely associated with the radio-metric
concept of radiance.