Any device(s) employed to partially (e.g., laser attenuative translucent window materials) or fully (e.g., opaque curtains) diminish or restrict the transmission of incipient laser light.

Beam Bender

Hardware assembly or optical device, such as a mirror, capable of changing laser beam direction; used to re-point the beam and in folded, compact delivery systems.

Beam Divergence

The increase in the diameter of the laser beam with distance from the exit aperture, based on the full angle at the point where the irradiance (or radiant exposure for pulsed lasers) is 1/e times the maximum value. Symbol: Ф

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 of vertically polarized light. Non-standard on industrial lasers, but a must if polarization is desired.


The visual sensation of the luminous power of a light beam, as opposed to scientifically measured power of the beam.