Laser Glossary (A-B)

ABLATION: The removal of material or tissue by melting, evaporation, or vaporization.

ABSORB: To transform radiant energy into a different form, usually with a resultant rise in temperature.

ABSORBANCE: The ability of a medium to absorb radiation depending on temperature and wavelength. Expressed as the negative common logarithm of the transmittance.

ABSORPTION COEFFICIENT: The amount of radiant energy absorbed per unit or path-length.

ACTIVE MEDIUM: A medium in which lasing will take place, rather than absorption, at a given wavelength.

AFOCAL: Literally, “without a focal length”; an optical system with its object and image point at infinity.

AMPLIFICATION: The growth of the radiation field in the laser resonator cavity. As the light wave bounces back and forth between the cavity mirrors, it is amp stimulated emission on each pass through the active medium.

AMPLITUDE: The maximum value of the electromagnetic wave, measured from the mean to the extreme; put simply, the height of the wave. (See drawing under “POLARIZATION.”)

ANGLE OF INCIDENCE: see “INCIDENT LIGHT.”

ANGSTROM UNIT: A unit of measurement for a wavelength of light (written Å), equal to one ten billionth of a meter (10^-10 meter). Occasionally still used.

ANODE: An electrical element in laser excitation which attracts electrons from a cathode. An anode can be cooled directly by water or by radiation.

AR COATINGS: Anti-reflection coatings, used on the backs of laser output mirrors to suppress unwanted multiple reflections which reduce power.

AUTOCOLLIMATOR: A single instrument combining the functions of a telescope and a collimator to detect small angular displacements of a mirror by means of its own collimated light.

AXIAL-FLOW LASER: The simplest and most efficient of the gas lasers. An axial flow of gas is maintained through the tube to replace those gas molecules depleted by the electrical discharge used to excite the gas molecules to the lasing state. (See “GAS DISCHARGE LASER.”)

AXIS, OPTICAL AXIS: The optical center-line for a lens system; the line passing through the centers of curvature of the optical surfaces of a lens.

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 DIAMETER: The diameter of that portion of the beam which contains 86% of the output power.

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

BEAM SPLITTING: Optically splitting a laser beam into two or more beams, allowing work on more than one side of a part at the same time—but at somewhat less power than with a multiple-output beam system.

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.

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

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