Glossary
aberration: Deviation from what is normal; in optics, defects of a lens system that cause its image to deviate from normal.
absorption: Transformation of radiant energy to a different form of energy by interaction with matter. Or, the loss of light as it passes through a material.
accessible emission limit (AeL): The maximum accessible emission level permitted within a particular class.
accessible optical radiation: Optical radiation to which the human eye or skin may be exposed for the condition (operation, maintenance, or service) specified.
active medium: A medium in which stimulated emission will take place at a given wavelength.
alpha max (αmax): The angular limit beyond which extended source MPEs (maximum permissible exposures) for a given exposure duration are expressed as a constant radiance or integrated radiance. This value is defined as 100 mrad.
alpha min (αmin): See limiting angular subtense.
aperture: An opening or window through which radiation passes.
aphakic: Term describing an eye in which the crystalline lens is absent.
apparent visual angle: The angular subtense of the source as calculated from source size and distance from the eye. It is not the beam divergence of the source.
attenuation: The decrease in the radiant flux as it passes through an absorbing or scattering medium.
authorized personnel: Individuals approved by management to install, operate, or service laser equipment.
average power: The total energy in an exposure or emission divided by the duration of the exposure or emission.
aversion response: Closure of the eyelid, eye movement, pupillary constriction, or movement of the head to avoid an exposure to a noxious stimulant or bright light. In this standard, the aversion response to an exposure from a bright laser source is assumed to occur within 0.25 seconds, including the blink reflex time.
beam: A collection of rays characterized by direction, diameter (or dimensions), and divergence (or convergence).
beam diameter: The distance between diametrically opposed points in that cross section of a beam where the power per unit area is 1/e (0.368) times that of the peak power per unit area.
beam divergence (ϕ): See divergence.
beam expander: An optical device that increases beam diameter while decreasing beam divergence (spread). Its simplest form consists of two lenses, the first to diverge the beam and the second to recollimate it. Also called an upcollimator.
beam splitter: An optical device that uses controlled reflection to produce two beams from a single incident beam.
blink reflex: The blink reflex is the involuntary closure of the eyes as a result of stimulation by an external event, such as an irritation of the cornea or conjunctiva, a bright flash, the rapid approach of an object, or an auditory stimulus or with facial movements. The ocular aversion response may include a blink reflex.
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 for one axis of plane polarized light. Nonstandard on industrial lasers, but some polarizing element must be used if a polarized output is desired.
calorimeter: A device for measuring the total amount of energy absorbed from a source of electromagnetic radiation.
carcinogen: An agent potentially capable of causing cancer.
coagulation: The process of congealing by an increase in viscosity characterized by a condensation of material from a liquid to a gelatinous or solid state.
coherent: A light beam is said to be coherent when the electric vector at any point in it is related to that at any other point by a definite, continuous function.
collateral radiation: Any electromagnetic radiation, except laser radiation, emitted by a laser or laser system that is physically necessary for its operation.
collecting optics: Lenses or optical instruments having magnification and thereby producing an increase in energy or power density. Such devices may include telescopes, binoculars, microscopes, or loupes.
collimated beam: Effectively, a parallel beam of light with very low divergence or convergence.
conjunctival discharge (of the eye): Increased secretion of mucus from the surface of the eyeball.
continuous wave (CW): The output of a laser that is operated in a continuous rather than a pulsed mode. In this standard, a laser operating with a continuous output for a period of 0.25 seconds or longer is regarded as a CW laser.
controlled area: An area where the occupancy and activity of those within are subject to control and supervision for the purpose of protection from radiation hazards.
cornea: The transparent outer coat of the human eye that covers the iris and the crystalline lens. The cornea is the main refracting element of the eye.
critical frequency: The pulse-repetition frequency above which the laser output is considered CW. For a 10-second exposure to a small source, the critical frequency is 55 kHz for wavelengths between 0.4 and 1.05 µm and 20 kHz for wavelengths between 1.05 and 1.4 µm.
cryogenics: The branch of physical science dealing with very low temperatures.
denaturation: Functional modification of the properties of protein by structural alteration via heat or photochemical processes.
depigmentation: The removal of the pigment of melanin granules from human tissues.
dermatology: A branch of medical science that deals with the skin, its structure, functions, and diseases.
dichroic filter: Filter that allows selective transmission of colors of desired wavelengths.
diffuse reflection: Change of the spatial distribution of a beam of radiation when it is reflected in many directions by a surface or by a medium.
diopter: A measure of the power of a lens, defined as 1/f0, where f0 is the focal length of the lens in meters.
divergence (ϕ): For the purposes of this standard, divergence is taken as the plane angle projection of the cone that includes 1 − 1/e (i.e., 63.2%) of the total radiant energy or power. The value is expressed in radians or milliradians.
duty cycle: Ratio of total on duration to total exposure duration for a repetitively pulsed laser.
effective energy (Qeff): Energy, in joules, through the applicable measurement aperture.
effective power (ΦFeff): Power, in watts, through the applicable measurement aperture.
electromagnetic radiation: The flow of energy consisting of orthogonally vibrating electric and magnetic fields lying transverse to the direction of propagation. X-ray, ultraviolet, visible, infrared, and radio waves occupy various portions of the electromagnetic spectrum and differ only in frequency, wavelength, and photon energy.
embedded laser: An enclosed 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 because of the engineering features limiting accessible emission.
enclosed laser: A laser that is contained within a protective housing of itself or of the laser or laser system in which it is incorporated. Opening or removing of the protective housing provides additional access to laser radiation above the applicable MPE than possible with the protective housing in place (an embedded laser is an example of one type of enclosed laser).
endoscope: An instrument utilized for the examination of the interior of a canal or hollow organ.
energy: The capacity for doing work. Energy content is commonly used to characterize the output from pulsed lasers and is generally expressed in joules (J).
epidemiology: A branch of medical science that deals with the incidence, distribution, and control of disease in a population.
epithelium (of the cornea): The layer of cells forming the outer epidermis of the cornea.
erythema: Redness of the skin because of congestion of the capillaries.
extended source: A source of optical radiation with an angular subtense at the cornea larger than αmin.
eye-safe laser: A Class 1 laser product. Because of the frequent misuse of the term eye-safe wavelength to mean retina safe (e.g., at 1.5–1.6 µm) and eye-safe laser to refer to lasers emitting outside the retinal hazard region in this spectral region, the term eye safe can be a misnomer. Hence, the use of eye-safe laser is discouraged.
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.
femtoseconds: 10−15 seconds. 1 femtoseconds = 0.000,000,000,000,001 seconds.
F-number: The focal length of lens divided by its usable diameter. In the case of a laser, the usable diameter is the diameter of the laser beam or a smaller aperture that restricts a laser beam.
fiber optics: A system of flexible quartz or glass fibers that uses total internal reflection to pass light through thousands of glancing (total internal) reflections.
flashlamp: A tube typically filled with krypton or xenon. Produces a high-intensity white light in short-duration pulses.
fluorescence: The emission of light of a particular wavelength resulting from absorption of energy, typically from light of shorter wavelengths.
focal length: The distance, measured in centimeters, from the secondary nodal point of a lens to the secondary focal point. For a thin lens imaging a distant source, the focal length is the distance between the lens and the focal point.
focal point: The point toward which radiation converges or from which radiation diverges or appears to diverge.
fundus: See ocular fundus.
funduscopic: Examination of the fundus (rear) of the eye.
gain: Amplification.
gas laser: A type of laser in which the laser action takes place in a gas medium.
gated pulse: A discontinuous burst of laser light made by timing (gating) a CW output—usually in fractions of a second.
Gaussian curve: Statistical curve showing a peak with normal even distribution on either side. Maybe either a sharp peak with steep sides or a blunt peak with shallower sides. Used to show power distribution in a beam. The concept is important in controlling the geometry of the laser impact.
ground state: Lowest energy level of an atom.
half-power point: The value on either the leading or trailing edge of a laser pulse at which the power is one-half of its maximum value.
heat sink: A substance or device used to dissipate or absorb unwanted heat energy.
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.
hertz (Hz): The unit that expresses the frequency of a periodic oscillation in cycles per second.
image: The optical reproduction of an object; produced by a lens or mirror. A typical positive lens converges rays to form a real image that can be photographed. A negative lens spreads rays to form a virtual image that cannot be projected.
incident light: A ray of light that falls on the surface of a lens or any other object. The angle of incidence is the angle made by the ray perpendicular (normal) to the surface.
infrared (IR): The region of the electromagnetic spectrum between the long-wavelength extreme of the visible spectrum (about 0.7 µm) and the shortest microwaves (about 1 mm).
infrared (IR) radiation: Electromagnetic radiation with wavelengths that lie within the range 0.7 µm to 1 mm.
installation: Placement and connection of laser equipment at the appropriate site to enable intended operation.
integrated radiance: The integral of the radiance over the exposure duration; expressed in joules per square centimeter per steradian (J·cm−2·sr−1).
intrabeam viewing: The viewing condition by which the eye is exposed to all or part of a laser beam.
ionizing radiation: Electromagnetic radiation having a sufficiently large photon energy to directly ionize atomic or molecular systems with a single quantum event.
iris: The circular pigmented membrane that lies behind the cornea of the human eye. The iris is perforated by the pupil.
irradiance: Radiant power incident per unit area on a surface; expressed in watts per square centimeter (W·cm−2). Synonym: power density.
joule (J): A unit of energy. 1 joule = 1 watt·second.
KtP (potassium titanyl phosphate): A crystal used to change the wavelength of an Nd:YAG laser from 1060 nm (infrared) to 532 nm (green).
Lambertian surface: An ideal surface with emitted or reflected radiance that is independent of the viewing angle.
laser: A device that produces radiant energy predominantly by stimulated emission. Laser radiation may be highly coherent temporally, spatially, or both. An acronym for light amplification by stimulated emission of radiation.
laser barrier: A device used to block or attenuate incident direct or to diffuse laser radiation. Laser barriers are frequently used during times of service to the laser system when it is desirable to establish a boundary for a temporary (or permanent) laser-controlled area.
laser diode: A laser employing a forward-biased semiconductor junction as the active medium. Synonyms: injection laser; semiconductor laser.
laser pointer: A Class 2 or Class 3A laser product that is usually handheld that emits a low-divergence visible beam of less than 5 mW and is intended for designating specific objects or images during discussions, lectures, or presentations as well as for the aiming of firearms or other visual targeting practice.
laser safety officer (LSo): One who has authority to monitor and enforce the control of laser hazards and effect the knowledgeable evaluation and control of laser hazards.
laser system: An assembly of electrical, mechanical, and optical components that includes a laser.
lesion: An abnormal change in the structure of an organ or part because of injury or disease.
limiting angular subtense (αmin): The apparent visual angle that divides small-source viewing from extended-source viewing, αmin is defined as 1.5 mrad.
limiting aperture diameter (Df): The diameter of a circle over which irradiance or radiant exposure is averaged for purposes of hazard evaluation and classification from.
limiting cone angle (γ): The cone angle through which radiance or integrated radiance is averaged when photochemical effects are considered in hazard evaluation and laser classification.
limiting exposure duration (Tmax): An exposure duration that is specifically limited by the design or intended use.
macula: The small, uniquely pigmented, specialized area of the retina of the eye that, in normal individuals, is predominantly employed for acute central vision (i.e., area of best visual acuity).
magnified viewing: Viewing a small object through an optic that increases the apparent object size. This type of optical system can make a diverging laser beam more hazardous (e.g., using a magnifying optic to view an optical fiber with a laser beam emitted).
maintenance: Performance of those adjustments or procedures (specified in user information provided by the manufacturer with the laser or laser system) that are to be performed by the user to ensure the intended performance of the product.
maximum permissible exposure (MPe): The level of laser radiation to which a person may be exposed without hazardous effect or adverse biological changes in the eye or skin.
measurement aperture: The aperture used for classification of a laser to determine the effective power or energy that is compared to the AEL for each class.
meter: A unit of length in the International System of Units currently defined as the length of a path traversed in vacuum by light during a period of 1/299792458 seconds. Typically, the meter is subdivided into the following units: centimeter (cm) = 10−2 m; millimeter (mm) = 10−3 m; micrometer (µm) = 10−6 m; nanometer (nm) = 10−9 m.
minimum viewing distance: The minimum distance at which the eye can produce a focused image of a diffuse source, usually assumed to be 10 cm.
mode: A term used to describe how the power of a laser beam is geometrically distributed across the cross section of the beam. Also used to describe the operating style of a laser such as continuous or pulsed.
mode locked: A method of producing laser pulses in which short pulses (~10−12 seconds) are produced and emitted in bursts or a continuous train.
modulation: The ability to superimpose an external signal on the output beam of the laser as a control.
monochromatic light: Theoretically, light consisting of just one wavelength. No light is absolutely single frequency since it will have some bandwidth. Lasers provide the narrowest of bandwidths that can be achieved.
multimode: Laser emission at several closely spaced frequencies.
nanometer (nm): A unit of length in the International System of Units equal to one-billionth of a meter. A measure of length, with 1 nm equal to 10−9 m; the usual measure of light wavelengths. Visible light ranges from about 400 nm in the purple to about 760 nm in the deep red.
nanosecond (ns): One-billionth (10−9) of a second. Longer than a picosecond or femtosecond but shorter than a microsecond. Associated with Q-switched lasers.
nd:glass laser: A solid-state laser of neodymium:glass offering high power in short pulses. An Nd-doped glass rod used as a laser medium to produce 1064-nm light.
nd:yAG (neodymium:yttrium aluminum garnet) laser: A synthetic crystal used as a laser medium to produce 1064-nm light.
near-field imaging: A solid-state laser imaging technique offering control of spot size and hole geometry, adjustable working distance, uniform energy distribution, and a wide range of spot sizes.
neMA: Acronym for National Electrical Manufacturers’ Association, a group that defines and recommends safety standards for electrical equipment.
neodymium (nd): The rare earth element that is the active element in Nd:YAG lasers and Nd:glass lasers.
noise: Unwanted minor currents or voltages in an electrical system.
nominal hazard zone (nHz): 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): The distance along the axis of the unobstructed beam from a laser, fiber end, or connector to the human eye beyond which the irradiance or radiant exposure, during installation or service, is not expected to exceed the appropriate MPE.
non-beam hazard: A class of hazards that result from factors other than direct human exposure to a laser beam.
ocular fundus: The interior posterior surface of the eye (the retina) as seen on ophthalmoscopic examination.
operation: The performance of the laser or laser system over the full range of its intended functions (normal operation).
ophthalmoscope: An instrument for examining the interior of the eye.
optical cavity (resonator): Space between the laser mirrors where lasing action occurs.
optical density (oD): A logarithmic expression for the attenuation produced by an attenuating medium, such as an eye protection filter. The logarithm to the base 10 of the reciprocal of the transmittance: OD = log10 (Ei/Et), where OD is optical density, Ei incident beam irradiance (W/cm2) worst-case exposure, and Et transmitted beam irradiance (MPE limit in W/cm2).
optical fiber: A filament of quartz or other optical material capable of transmitting light along its length by multiple internal reflections 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 nm) that falls in the region of transmittance of the human eye.
optically aided viewing: Viewing with a telescopic or magnifying optic. Under certain circumstances, viewing with an optical aide can increase the hazard from a laser beam. See telescopic viewing; magnified viewing.
optically pumped lasers: A type of laser that derives energy from another light source such as a xenon or krypton flashlamp or other laser source.
output coupler: Partially reflective mirror in laser cavity that allows emission of laser light.
output power: The energy per second measured in watts emitted from the laser in the form of coherent light.
photochemical effect: An effect (e.g., biological effect) produced by a chemical action brought about by the absorption of photons by molecules that directly alters the molecule. For example, one photon of sufficient energy can alter a single molecule. Such effects are generally important in the shorter visible and ultraviolet regions of the optical spectrum. The threshold radiant exposure is constant over a wide range of exposure durations (the Bunsen–Roscoe law).
photophobia: An unusual intolerance of light. Also, an aversion to light usually caused by physical discomfort on exposure to light.
photosensitizers: Substances that increase the sensitivity of a material to irradiation by electromagnetic energy.
pigment epithelium (of the retina): The layer of cells that contains brown or black pigment granules next to and behind the rods and cones.
plasma radiation: Black body radiation generated by luminescence of matter in a laser-generated plume.
point source: No longer used. See small source.
power: The rate at which energy is emitted, transferred, or received. Unit: watts (joules per second).
protective housing: An enclosure surrounding the laser or laser system that prevents access to laser radiation above the applicable MPE level. The aperture through which the useful beam is emitted is not part of the protective housing. The protective housing may enclose associated optics and a workstation and limits access to other associated radiant energy emissions and to electrical hazards associated with components and terminals.
pulse duration: The length of a laser pulse, usually measured as the time interval between the half-power points on the leading and trailing edges of the pulse.
pulse-repetition frequency (PrF): The number of pulses occurring per second; expressed in hertz.
pulsed laser: A laser that delivers its energy in the form of a single pulse or a train of pulses. In this standard, the duration of a pulse is less than 0.25 seconds.
pump: To excite the lasing medium. See optical pumping; pumping.
pumped medium: Energized laser medium.
pumping: Addition of energy (thermal, electrical, or optical) into the atomic population of the laser medium; necessary to produce a state of population inversion.
pupil: The variable aperture in the iris through which light travels to the interior of the eye.
q-switch: A device for producing very short (~10–250 nanoseconds), intense laser pulses by enhancing the storage and dumping of electronic energy in and out of the lasing medium, respectively.
q-switched laser: A laser that emits short (~10–250 nanoseconds), high-power pulses by means of a Q-switch.
radian (rad): A unit of angular measure equal to the angle subtended at the center of a circle by an arc with a length that is equal to the radius of the circle. 1 radiañ57.3°; 2π radians = 360°.
radiance: Radiant flux or power output per unit solid angle per unit area expressed in watts per centimeter squared per steradian (W·cm−2·sr−1).
radiant energy: Energy emitted, transferred, or received in the form of radiation. Unit: joules (J).
radiant exposure: Surface density of the radiant energy received; expressed in units of joules per centimeter squared (J·cm−2).
radiant flux: Power emitted, transferred, or received in the form of radiation. Unit: watts (W). Also called radiant power.
radiant intensity: Quotient of the radiant flux leaving a source and propagated into an element of solid angle containing the direction, by the element of solid angle. Radiant intensity is expressed in units of watts per steradian (W·sr−1).
radiant power: Power emitted, transferred, or received in the form of radiation; expressed in watts (W). Synonym: radiant flux.
radiometry: A branch of science that deals with the measurement of radiation.
rayleigh scattering: Scattering of radiation in the course of its passage through a medium containing particles with sizes that are small compared with the wavelength of the radiation.
reflectance: The ratio of total reflected radiant power to total incident power. Also called reflectivity.
reflection: Deviation of radiation following incidence on a surface.
refraction: The bending of a beam of light in transmission through an interface between two dissimilar media or in a medium with a refractive index that is a continuous function of position (graded index medium).
refractive index (of a medium): Denoted by n, the ratio of the velocity of light in vacuum to the phase velocity in the medium. Synonym: index of refraction.
repetitive pulse laser: A laser with multiple pulses of radiant energy occurring in a sequence.
resonator: 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.
retina: The sensory membrane that receives the incident image formed by the cornea and lens of the human eye. The retina lines the inside of the eye.
retinal hazard region: Optical radiation with wavelengths between 0.4 and 1.4 µm, for which the principal hazard is usually to the retina.
rotating lens: A beam delivery lens designed to move in a circle and thus rotate the laser beam around a circle.
ruby: The first laser type; a crystal of sapphire (aluminum oxide) containing trace amounts of chromium oxide.
safety latch: A mechanical device designed to slow direct entry to a controlled area.
scanning laser: A laser having a time-varying direction, origin, or pattern of propagation with respect to a stationary frame of reference.
scintillation: The rapid changes in irradiance levels in a cross section of a laser beam.
secured enclosure: An enclosure to which casual access is impeded by an appropriate means, such as a door secured by a magnetically or electrically operated lock or latch, or by fasteners that need a tool to remove.
service: The performance of those procedures or adjustments described in the manufacturer’s service instructions that may affect any aspect of the performance of the laser or laser system.
shall: The word shall is to be understood as mandatory.
should: The word should is to be understood as advisory.
small source: In this document, a source with an angular subtense at the cornea equal to or less than alpha min (αmin), that is, less than or equal to 1.5 mrad. This includes all sources formerly referred to as point sources and meeting small-source viewing (formerly called point source or intrabeam viewing) conditions.
small-source viewing: The viewing condition by which the angular subtense of the source αmin is equal to or less than the limiting angular subtense αmin.
solid angle: The three-dimensional angular spread at the vertex of a cone measured by the area intercepted by the cone on a unit sphere with a center that is the vertex of the cone. Solid angle is expressed in steradians (sr).
source: A laser or a laser-illuminated reflecting surface.
spectator: An individual who wishes to observe or watch a laser or laser system in operation and who may lack the appropriate laser safety training.
specular reflection: A mirror-like reflection.
standard operating procedure (SoP): Formal written description of the safety and administrative procedures to be followed in performing a specific task.
steradian (sr): The unit of measure for a solid angle. There are 4π steradians about any point in space.
stromal haze (of the cornea): Cloudiness in the connective tissue or main body of the cornea.
surface exfoliation (of the cornea): A stripping or peeling off of the surface layer of cells from the cornea.
synergism: A condition in which the combined effect is greater than the sum of the effects of individual contributors.
T1: The exposure duration (time) at which MPEs based on thermal injury are replaced by MPEs based on photochemical injury to the retina.
T2: The exposure duration (time) beyond which extended-source MPEs based on thermal injury are expressed as a constant irradiance.
telescopic viewing: Viewing an object from a long distance to increase its visual size. These systems generally collect light through a large aperture, magnifying hazards from large-beam, collimated lasers.
teM: Abbreviation for transverse electromagnetic modes. Used to designate the cross-sectional shape of the beam. The radial distribution of intensity across a beam as it exits the optical cavity.
teM00: The lowest-order mode possible with a bell-shaped (Gaussian) distribution of light across the laser beam.
thermal effect: An effect brought about by the temperature elevation of a substance (e.g., biological tissue). Photocoagulation of proteins resulting in a thermal burn is an example. The threshold radiant exposure is dependent on the duration of exposure and heat transfer from the heated area.
threshold limit (tL): The term is applied to laser protective eyewear filters, protective windows, and barriers. The TL is an expression of the resistance factor for beam penetration of a laser protective device. This is generally related by the TL of the protective device (expressed in W·cm−2 or J·cm−2). It is the maximum average irradiance (or radiant exposure) at a given beam diameter for which a laser protective device (e.g., filter, window, barrier) provides adequate beam resistance. Thus, laser exposures delivered on the protective device at or below the TL will limit beam penetration to levels at or below the applicable MPE.
Tmax: See limiting exposure duration.
tmin: For a pulsed laser, the maximum duration for which the MPE is the same as the MPE for a 1-nanosecond exposure. For thermal biological effects, this corresponds to the thermal confinement duration during which heat flow does not significantly change the absorbed energy content of the thermal relaxation volume of the irradiated tissue (e.g., tmin is 18 microseconds in the spectral region from 0.4 to 1.05 µm and is 50 microseconds between 1.050 and 1.400 µm).
tonometry: Measurement of the pressure (tension) of the eyeball.
transmission: Passage of radiation through a medium.
transmittance: The ratio of transmitted power to incident power.
tunable dye laser: A laser with an active medium that is a liquid dye, pumped by another laser or flashlamps, to produce various colors of light. The color of light may be tuned by adjusting optical tuning elements or changing the dye used.
tunable laser: A laser system that can be tuned to emit laser light over a continuous range of wavelengths or frequencies.
ultraviolet radiation: Electromagnetic radiation with wavelengths shorter than those of visible radiation; for the purpose of this standard, 0.18–0.4 µm.
uncontrolled area: An area where the occupancy and activity of those within is not subject to control and supervision for the purpose of protection from radiation hazards.
viewing portal: An opening in a system that allows the user to observe the chamber. All viewing portals and display screens included as an integral part of a laser system must incorporate a suitable means to maintain the laser radiation at the viewing position at or below the applicable MPE (eye safe) for all conditions of operation and maintenance. It is essential that the materials used for viewing portals and display screens do not support combustion or release toxic vapors following exposure to laser radiation.
viewing window: Visually transparent parts of enclosures that contain laser processes. It may be possible to observe the laser processes through the viewing windows.
visible radiation (light): The term is used to describe electromagnetic radiation that can be detected by the human eye. This term is commonly used to describe wavelengths that lie in the range 0.4–0.7 µm.
watt (W): The unit of power or radiant flux. 1 watt = 1 joule per second.
watt/cm2: A unit of irradiance used in measuring the amount of power per area of absorbing surface or per area of CW laser beam.
wave: A sinusoidal undulation or vibration; a form of movement by which all radiant electromagnetic energy travels.
wavelength: The length of the light wave, usually measured from crest to crest, that determines its color. Common units of measurement are the micrometer (micron), the nanometer, and (earlier) the angstrom unit.
window: A piece of glass (or other material) with plane parallel sides that admits light into or through an optical system and excludes dirt and moisture.
work practices: Procedures used to accomplish a task.
yAG (yttrium aluminum garnet): A widely used solid-state crystal that is composed of yttrium and aluminum oxides, which is doped with a small amount of the rare-earth neodymium.
z-cavity: A term referring to the shape of the optical layout of the tubes and resonator inside a laser.