ABSORB To transform radiant energy into a different form, with a resultant
rise in temperature.
ABSORPTION Transformation of radiant energy to a different form of energy by
the interaction of matter, depending on temperature and wavelength.
ABSORPTION COEFFICIENT Factor describing light's ability to be absorbed per
unit of path length.
ACCESSIBLE EMISSION LEVEL The magnitude of accessible laser (or collateral)
radiation of a specific wavelength or emission duration at a particular point
as measured by appropriate methods and devices. Also means radiation to which
human access is possible in accordance with the definitions of the laser's hazard
classification.
ACCESSIBLE EMISSION The maximum accessible emission level.
ACCESSIBLE EMISSION LIMIT (AEL) permitted within a particularly class. In ANSI
Z- 136.1, AEL is determined as the product of Accessible Emission Maximum Permissible
Exposure limit (MPE) and the areaof the limiting aperture (7mm for visible and
near infrared lasers).
ACTIVE MEDIUM Collection of atoms or molecules capable of undergoing stimulated
emission at a given wavelength.
AFOCAL Literally, "without a focal length"; an optical system with its object
and image point at infinity.
AIMING BEAM A laser (or other light source) used as a guide light. Used coaxially
with infrared or other invisible light may also be a reduced level of the actual
laser used for surgery or for other applications.
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 amplified
by stimulated emission on each pass through the active medium.
AMPLITUDE The maximum value of the electro-magnetic wave, measured from the
mean to the extreme; simply stated: the height of the wave.
ANGLE OF INCIDENCE See Incident Ray
ANGSTROM UNIT A unit of measure of wavelength dual to 10(-10) meter, 0.1 nanometer,
or 10(-4) micrometer, no longer widely used nor recognized in the SI system of
units.
ANODE An electrical element in laser excitation which attracts electrons from
a cathode.
APERTURE An opening through which radiation can pass.
APPARENT VISUAL ANGLE The angular subtense of the source as calculated from
the source size and distance from the eye. It is not the beam divergence of the
source.
AR COATINGS Antireflection coatings used on optical components to suppress
unwanted reflections.
ARGON A gas used as a laser medium. It emits blue/green light primarily at
448 and 515 nm.
ARTICULATED ARM CO(2) laser beam delivery device consisting of a series of
hollow tubes and mirrors interconnected in such a manner as to maintain alignment
of the laser beam along the path of the arm.
ATTENUATION The decrease in energy (or power) as a beam passes through an absorbing
or scattering medium.
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.
AVERAGE POWER The total energy imparted during exposure divided by the exposure
duration.
AVERSION RESPONSE Movement of the eyelid or the head to avoid an exposure to
a noxious stimulant, bright light. It can occur within 0.25 seconds, and it includes
the blink reflex time.
AXIAL-FLOW LASER A laser in which 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. See gas discharge laser.
AXICON LENS A conical lens which, when followed by a conventional lens, can
focus laser light to a ring shape.
AXIS, OPTICAL AXIS The optical centerline for a lens system; the line passing
through the centers of curvature of the optical surfaces of a lens.
