This glossary has been developed specifically to aid the reader of this volume in interpreting unfamiliar terms. The definitions are intended to have a practical, rather than formal, presentation. That is, they may be specifically oriented toward the use of the word in the electro optics sciences, rather than a more general definition that would be found in a generic encyclopedia or dictionary.

A

?rad

Microradians, millionths of a radian.

?W

Microwatts, millionths of a watt.

aberrated

Defines a range of degradations in image quality. Aberrations include, but are not limited to, field curvature, distortion, coma, chromatic aberration, and astigmatism.

absorptance

The property of a material that acts to reduce the amount of radiation traversing through a section of the material, it is measured as the fraction of radiation absorbed. Generally, the bulk absorptance of radiation by a material follows Beer's law.

acousto-optic tunable filter

A special type of filter that works by exploiting the properties of its material; namely, that the index of refraction depends on strain within the material

adaptive optics

Optical subsystems with the ability to change the wavefront in real time. They are generally used to compensate for atmospheric turbulence.

ADC

Analog-to-digital converier (or conversion).

afocal

Describes an optical system that does not form a focus, such as often employed in laser beam expanders. Such optics accept or project a light field and produce an unfocused beam.

airmass

A term frequently used by astronomers, referring to the path length in the atmosphere through...