Glossary > A



To transform radiant energy into a different form, with a resultant change in temperature.


Transformation of radiant energy to a different form of energy by the action 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. Also means radiation to which human access is possible in accordance with the definitions of the laser’s hazard classification.

Accessible emission limit (AEL)

The maximum accessible emission level permitted within a particular class of lasers. In ANSI Z-136.1, AEL is determined as the product of Accessible Emission Level Maximum Permissible Exposure (MPE) limit and the area of the limiting aperture (7mm for visible and near infrared lasers).

Achromatic lens

A usually two-element lens that is corrected for chromatic aberration to bring two specified or distinct wavelengths to a common focal point.

Active medium

Collection of atoms capable of undergoing stimulated emission at a given wavelength.


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, an aiming beam may also be a reduced level of the actual laser used for surgery or for other applications.

Ambient noise

The noise at a given location (such as in a room, a compartment, or a place outdoors), usually a composite of a number of sources.

Ambient temperature

The prevailing temperature of air or other media in a designated area, particularly the area surrounding an object.


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.


The maximum value of the electromagnetic wave, measured from the mean to the extreme. Stated simply, the height of the wave.

Analog modulation

Analog modulation is a type of modulation that requires an analog input signal to vary the output power of a laser. Our analog lasers are capable of modulation from CW to 20MHz. A benefit of analog modulation is that it allows users to adjust a laser’s output to a desired level from

Analog signal

A continuously varying signal (voltage or current), not pulsed or discrete in nature.

Anamorphic correction

An optical technique using one or two prisms to change an elliptical laser beam into a round beam.

Angstrom unit

A unit of measurement of wavelength equal to 10-10 meter, 0.1 nanometer, or 10-4 micrometer. No longer widely used or recognized in the SI system of units.

Angular drift

Any unintended change in direction of the beam before, during, and after warm-up, measured in mrad.

Antireflection coating

A thin layer of material applied to the surface of a lens to reduce reflected energy.


An electrical element in laser excitation that attracts electrons from a cathode.

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.


A passageway through which radiation or matter may pass.

AR coatings

Antireflection coatings used on optical components to suppress unwanted reflections off the surfaces.


A gas used as a laser medium. It emits blue/green light primarily at 448 and 515 nm.

Articulated arm

CO2 laser beam delivery device consisting of a series of hollow tubes and mirrors interconnected so as to maintain alignment of the laser beam along the path of the arm.

Astigmatic correction

An optical technique using a cylindrical lens to correct for the astigmatism inherent in laser diodes so that emissions from both the parallel and perpendicular planes come to focus at the same image plane.


A lens aberration in which light rays from a single point fail to converge in a single focal point.


The decrease in energy (or power) as a beam passes through an absorbing or scattering medium.


An electronic transducer that reduces the amplitude of a signal without distorting its waveform.


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.

Automatic power control mode

Laser diode drivers operating in this mode have a photodiode mounted inside the laser diode package. The photodiode generates a feedback signal that allows gauging and adjustment of the current supply, keeping the output power of the laser constant over temperature changes and time.

Average power

The total energy imparted during exposure divided by the exposure duration.

Aversion response

Movement of the eyelid or the head to avoid exposure to a noxious stimulant (e.g., a bright light). It can occur within 0.25 seconds, and it includes the blink reflex time.

Axicon lens

A conical lens that, 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.

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