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

Optical device increasing beam diameter and reducing divergence. Result: A smaller focused spot for more distance between lens and part.

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.

An instrument which measures the heat generated by absorption of the laser beam—another way to measure laser power.