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Laser List of Terms


Laser List of Terms - Glossary - Lazer



to transform radiant energy into a different form, with a resultant rise in temperature


transformation of radiant energy to a different form of energy by the interaction of matter, depending on

temperature and wavelength

accessible emission limit (AEL)

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 radiation

laser radiation that can expose human eye or skin in normal usage


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


the opening through which laser radiation can pass


the decrease in energy (or power) as a beam passes through an absorbing

or scattering medium

average power

total energy of an exposure divided by the duration of the exposure

aversion response

action, such as closing of the eye or movement of the head, to avoid exposure to laser light

beam diameter

the distance between diametrically opposed points in the cross section of a circular beam where the

intensity is reduced by a factor of e=1(0.368) of the peak level (for safety standards). The value is

normally chosen at e=2(0.135) of the peak level for manufacturing specifications

beam divergence

angle of beam spread measured in radians or milliradians (1 milliradian = 3.4 minutes of arc or

approximately 1 mil). For small angles where the cord is approximately equal to the arc, the beam

divergence can be closely approximated by the ratio of the cord length (beam diameter) divided by the

distance (range) from the laser aperture


the visual sensation of the luminous intensity of a light source. The brightness of a laser beam is most

closely associated with the radio-metric concept of radiance.

continuous wave (CW) laser

a laser which with a continuous output that is greater than or equal to 0.25 watts


carbon dioxide

molecule used as a laser medium. Emits far energy at 10,600 nm (10.6 μm)

closed installation

any location where lasers are used which will be closed to unprotected personnel during laser operation

CO2 laser

a widely used laser in which the primary lasing medium is carbon dioxide gas. The output wavelength is

10.6 μm (10600 nm) in the far infrared spectrum. It can be operated in either CW or pulsed


a term describing light as waves which are in phase in both time and space. Monochromaticity and low

divergence are two properties of coherent light

collimated light

light rays that are parallel. Collimated light is emitted by many lasers. Diverging light may be collimated

by a lens or other device


ability of the laser beam to not spread significantly (low divergence) with distance

continuous mode

the duration of laser exposure is controlled by the user (by foot or hand switch)

continuous wave (CW)

constant, steady-state delivery of laser power

controlled area

any locale where the activity of those within are subject to control and supervision for the purpose of

laser radiation hazard protection

diffuse reflection

takes place when different parts of a beam incident on a surface are reflected over a wide range of angles

in accordance with Lambert's Law. The intensity will fall off as the inverse of the square of the distance

away from the surface and also obey a Cosine Law of reflection


the increase in the diameter of the laser beam with distance from the exit aperture. The value gives the

full angle at the point where the laser radiant exposure or irradiance

embedded laser

a laser with an assigned class number higher than the inherent capability of the laser system in which it is

incorporated, where the system's lower classification is appropriate to the engineering features limiting

accessible emission


act of giving off radiant energy by an atom or molecule


enclosed laser device

any laser or laser system located within an enclosure which does not permit hazardous optical radiation

emission from the enclosure. The laser inside is termed an "embedded laser"

energy (Q)

the capacity for doing work. Energy is commonly used to express the output from pulsed lasers and it is

generally measured in Joules (J). The product of power (watts) and duration (seconds). One watt second

= one Joule

excimer "Excited Dimer"

a gas mixture used as the active medium in a family of lasers emitting ultraviolet light

fail-safe interlock

an interlock where the failure of a single mechanical or electrical component of the interlock will cause

the system to go into, or remain in, a safe mode

gas discharge laser

a laser containing a gaseous lasing medium in a glass tube in which a constant flow of gas replenishes

the molecules depleted by the electricity or chemicals used for excitation

gas laser

a type of laser in which the laser action takes place in a gas medium

helium-neon (HeNe) laser

a laser in which the active medium is a mixture of helium and neon. Its wavelength is usually in the

visible range. Used widely for alignment, recording, printing, and measuring

infrared radiation

invisible electromagnetic radiation with wavelengths which lie within the range of 0.70 to 1000 μm.

These wavelengths are often broken up into regions: IR-A (0.7-1.4 μm), IR-B (1.4-3.0 μm) and IR-C

(3.0-1000 μm)

intrabeam viewing

the viewing condition whereby the eye is exposed to all or part of a direct laser beam or a specular



power per unit area, expressed in watts per square centimeter

laser accessories

the hardware and options available for lasers, such as secondary gases, Brewster windows, Q-switches

and electronic shutters

laser device

either a laser or a laser system

laser medium (Active Medium)

material used to emit the laser light and for which the laser is named


laser rod

a solid-state, rod-shaped lasing medium in which ion excitation is caused by a source of intense light,

such as a flash lamp. Various materials are used for the rod, the earliest of which was synthetic ruby


laser system

an assembly of electrical, mechanical and optical components which includes a laser. Under the Federal

Standard, a laser in combination with its power supply (energy source)


a curved piece of optically transparent material which, depending on its shape, is used to either converge

or diverge light


the range of electromagnetic radiation frequencies detected by the eye, or the wavelength range from

about 400 to 760 nm. The term is sometimes used loosely to include radiation beyond visible limits


acronym for Light Amplification by Stimulated Emission of Radiation. A laser is a cavity with mirrors

at the ends, filled with material such as crystal, glass, liquid, gas or dye. It produces an intense beam of

light with the unique properties of coherency, collimation, and monochromaticity

laser safety officer

one who has authority to monitor and enforce measures to control laser hazards and effect the

knowledgeable evaluation and control of laser hazards

limiting aperture

the maximum circular area over which radiance and radiant exposure can be averaged when determining

safety hazards


performance of those adjustments or procedures specified in user information provided by the

manufacturer with the laser or laser system, which are to be performed by the user to ensure the intended

performance of the product. It does not include operation or service as defined in this glossary

maximum permissible exposure (MPE)

the maximum level of laser radiation to which a human can be exposed without adverse biological

effects to the eye or skin

Nd:Glass laser

a solid-state laser of neodymium:glass offering high power in short pulses. A Nd-doped glass rod used as

a laser medium to produce 1064 nm light

Nd:YAG laser

Neodymium:Yttrium Aluminum Garnet. A synthetic crystal used as a laser medium to produce 1064 nm


Neodymium (Nd)

the rare earth element that is the active element in Nd:YAG laser and Nd:Glass lasers.


nominal hazard zone (NHZ)

the nominal hazard zone describes the space within which the level of the direct, reflected or scattered

radiation during normal operation exceeds the applicable MPE. Exposure levels beyond the boundary of

the NHZ are below the appropriate MPE level.

nominal ocular hazard distance (NOHD)

distance along the axis of the direct laser beam to the human eye beyond which the MPE of the laser

is not exceeded

optical cavity (Resonator)

space between the laser mirrors where lasing action occurs

optical density

a logarithmic expression for the attenuation produced by an attenuating medium, such as an eye

protection filter

optical fiber

a filament of quartz or other optical material capable of transmitting light along its length by multiple

internal reflection and emitting it at the end

optical pumping

the excitation of the lasing medium by the application of light rather than electrical discharge

optical radiation

ultraviolet, visible, and infrared radiation (0.35-1.4 μm) that falls in the region of transmittance of the

human eye

output power

the energy per second measured in watts emitted from the laser in the form of coherent light


the rate of energy delivery expressed in watts (Joules per second). Thus: 1 Watt = 1 Joule × 1 Sec

protective housing

a protective housing is a device designed to prevent access to radiant power or energy


a discontinuous burst of laser, light or energy, as opposed to a continuous beam. A true pulse achieves

higher peak powers than that attainable in a CW output

pulse duration

the "on" time of a pulsed laser, it may be measured in terms of milliseconds, microseconds, or

nanoseconds as defined by half-peak-power points on the leading and trailing edges of the pulse

pulsed laser

laser which delivers energy in the form of a single or train of pulses


to excite the lasing medium


pumped medium

energized laser medium


addition of energy (thermal, electrical, or optical) into the atomic population of the laser medium,

necessary to produce a state of population inversion

pulsed laser

laser which delivers energy in single or multiple pulses which are less than or equal to 0.25 watts in


radiant energy (Q)

energy in the form of electromagnetic waves usually expressed in units of Joules (watt-seconds)

radiant exposure (H)

the total energy per unit area incident upon a given surface. It is used to express exposure to pulsed laser

radiation in units of J/cm2

radiant power

laser power emitted, expressed in watts (W)


the return of radiant energy (incident light) by a surface, with no change in wavelength


the change of direction of propagation of any wave, such as an electromagnetic wave, when it passes

from one medium to another in which the wave velocity is different. The bending of incident rays as they

pass from one medium to another (e.g., air to glass)

repetitively pulsed laser

laser with multiple pulses with a pulse repetition frequency greater than or equal to 1 Hz


the mirrors (or reflectors) making up the laser cavity including the laser rod or tube. The mirrors reflect

light back and forth to build up amplification


the first laser type; a crystal of sapphire (aluminum oxide) containing trace amounts of chromium oxide

scanning laser

a laser having a time-varying direction, origin or pattern of propagation with respect to a stationary frame

of reference

secured enclosure

an enclosure to which casual access is impeded by an appropriate means (e.g., door secured by lock,

magnetically or electrically operated latch, or by screws)

semiconductor laser

a type of laser which produces its output from semiconductor materials such as GaAs



performance of adjustments, repair or procedures on a non-routine basis, required to return the

equipment to its intended state


the term source means either laser or laser-illuminated reflecting surface, i.e., source of light

specular reflection

mirror-like reflection

tunable laser

a laser system that can be "tuned" to emit laser light over a continuous range of wavelengths or


tunable dye laser

a laser whose active medium is a liquid dye, pumped by another laser or flash lamps, to produce various

colors of light. The color of light may be tuned by adjusting optical tuning elements and/or changing the

dye used

radiant energy

laser energy emitted, expressed in joules (J) ultraviolet radiation

electromagnetic radiation with wavelengths from180-400 nm

visible radiation

electromagnetic radiation which is visible to the human eye; wave lengths from 400-700 nm

ultraviolet (UV) radiation

electromagnetic radiation with wavelengths between soft X-rays and visible violet light, often broken

down into UV-A (315-400 nm), UV-B (280-315 nm), and UV-C (100-280 nm)

visible radiation (light)

electromagnetic radiation which can be detected by the human eye. It is commonly used to describe

wavelengths in the range between 400 nm and 700-780 nm


the length of the light wave, usually measured from crest to crest, which determines its color. Common

units of measurement are the micrometer (micron), the nanometer, and (earlier) the Angstrom unit


Yttrium Aluminum Garnet, a widely used solid-state crystal composed of yttrium and aluminum oxides

and a small amount of the rare earth neodymium