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These definitions are solely intended for the use in laser safety.
accessible optical radiation
amax (alpha max)
The angular limit beyond which
extended source MPEs for a given exposure duration are expressed as a constant
radiance or integrated radiance.
The apparent visual angle which
divides small-source viewing from extended-source viewing.
An opening (typically circular) through which radiation can pass.
The angular subtense of the source as calculated from source size and distance
from the eye - not a synonym for beam divergence.
The decrease in the radiant flux (power) as radiation passes through an
absorbing or scattering medium.
The total energy in an exposure or emitted divided by the duration of the
exposure or emission.
Closure of the eyelid, or movement of the head to avoid an exposure to a bright
A collection of rays characterized by direction, diameter (or dimensions) and
divergence (or convergence).
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 or
The full angle, expressed in
radians, of the beam spread measured between those points which include laser
energy or irradiance equal to 1/e of the maximum value.
Closure of the eyelid, or movement of the head to avoid an exposure to a bright
Correction factor which increases the MPE values in the near infrared (IR-A)
spectral band (700-1400 nm) based upon reduced absorption properties of melanin
pigment granules found in the skin and in the retina.
Correction factor which increases the MPE values in the red end of the visible
spectrum (550-700 nm), because of greatly reduced photochemical hazards.
Correction factor which increases the MPE values for ocular exposure because of
pre-retinal absorption of radiant energy in the spectral region between 1150 and
Correction factor used for calculating the extended source MPE for the eye from
the small source MPE, when the laser source subtends a visual angle exceeding
Correction factor which reduces the MPE for repetitively pulsed exposure of the
eye. This factor is not used for the skin.
An agent potentially capable of causing cancer.
The process of congealing by an increase in viscosity characterized by a
condensation of material from a liquid to a gelatinous or solid state.
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.
Any electromagnetic radiation, except laser radiation, emitted by a laser or
laser system which is physically necessary for its
Lenses or optical instruments (such
as telescopes, binoculars, or microscopes) having magnification and thereby
producing an increase in energy or power densities.
A nearly ôparallelö (very
low divergence or convergence) beam of light.
The output of a laser which is operated in a continuous (duration
>0.25 s) rather than a pulsed mode.
An area where the occupancy and activity of those within it is subject to
control and supervision.
The transparent outer coat of the human eye which covers the iris and the
crystalline lens. The cornea is the main
refracting element of the eye.
The pulse repetition frequency above
which the laser output is considered continuous wave (CW).
Functional modification of the properties of protein by structural alteration
via heat or photochemical processes.
The removal of the pigment of melanin granules from human tissues.
Change of the spatial distribution of a beam of radiation when it is reflected
in many directions by a surface or by a medium.
A measure of the power of a lens, defined as 1/fo, where fo
is the focal length of the lens in meters.
effective energy (Qeff)
Energy, in joules, through the
applicable measurement aperture.
effective magnification (Meff)
The optical magnification used in
laser safety calculations for aided viewing conditions. It is the reduction in
beam diameter from an optical viewing system that increases the hazard.
effective power (
Power, in watts, through the
applicable measurement aperture.
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, or
An enclosed laser with an assigned class
number higher than the inherent capability of the laser system in which it is
incorporated, where the systems lower classification is appropriate due to the
engineering features limiting accessible emission.
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 removal 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
The capacity for doing work. Energy
content is commonly used to characterize the output from pulsed lasers, and is
generally expressed in joules (J).
The layer of cells forming the outer surface of the cornea.
Redness of the skin due to congestion of the capillaries.
A source of laser radiation with an
angular subtense at the cornea larger than amin.
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.
The distance from the secondary nodal point of a lens to the primary focal
point. In a thin lens, the focal length
is the distance between the lens and the focal point.
The point toward which radiation converges or from which radiation diverges or
appears to diverge.
The interior posterior surface of
the eye (the retina), as seen upon ophthalmoscopic examination.
Examination of the fundus (rear) of the eye.
The value on either the leading or trailing edge of a laser pulse at which the
power is one-half of its maximum value.
The unit which expresses the frequency of a periodic oscillation in cycles per
The region of the electromagnetic
spectrum between the long-wavelength extreme of the visible spectrum (about 0.7
mm) and the shortest microwaves (about 1
Electromagnetic radiation with wavelengths which lie within the range 0.7 mm
to 1 mm.
The integral of the radiance over
the exposure duration, expressed in joules-per-square-centimeter -per-steradian
(J cm-2 sr-1).
The viewing condition whereby the
eye is exposed to all or part of a laser beam.
Electromagnetic radiation having a sufficiently large photon energy to directly
ionize atomic or molecular systems with a single quantum event.
Radiant power incident per unit area
upon a surface, expressed in watts-per-square-centimeter
Samples of type of various sizes printed on a card for testing close visual
acuity. An analogue of the Snellen chart
for distant visual acuity.
A unit of energy. 1 joule = 1 watt x 1
An ideal surface whose emitted or reflected radiance is independent of the
A device that produces radiant
energy predominantly by stimulated emission.
Laser radiation may be highly coherent temporally, or spatially, or both.
An acronym for Light
Amplification by Stimulated
Emission of Radiation.
A laser employing a forward-biased
semiconductor junction as the active medium.
Synonyms: injection laser;
One who has authority to monitor and enforce the control of laser hazards and
effect the knowledgeable evaluation and control of laser hazards.
An assembly of electrical, mechanical, and optical components which includes a
An abnormal change in the structure of an organ or part due to injury or
Electromagnetic radiation which can be detected by the human eye.
This term is commonly used to describe wavelengths which lie in the range 0.4 to
amin (limiting angular subtense)
The maximum diameter of a circle
over which radiance and radiant exposure is averaged for purposes of hazard
evaluation and classification.
An exposure duration which is specifically limited by the design or intended
A medium which absorbs or scatters radiation passing through it.
The small uniquely pigmented specialized area of the retina of the eye which in
normal individual is predominantly employed for acute central vision, i.e. area
of best visual acuity.
The level of laser radiation to which a person may be exposed without hazardous
effect or adverse biological changes in the eye or skin.
minimum viewing distance
The minimum distance at which the
eye can produce a focused image of a diffuse source, usually assumed to be 10
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)
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.
optically aided viewing
Viewing the laser source with an
optical device such as an eye loupe, hand magnifier, microscope, binoculars,
telescope, etc. Optically aided viewing
does not include viewing with corrective eyewear or with indirect image
optical density (OD)
Logarithm to the base ten of the reciprocal
of the transmittance. OD is a physical property of a substance.
An unusual intolerance of light. Also,
an aversion to light usually caused by physical discomfort upon exposure to
Substances which increase the sensitivity of a material to irradiation by
The layer of cells which contain brown or black pigment granules next to and
behind the rods and cones.
Black body radiation generated by luminescence of matter in a laser-generated
A source with an angular subtense at
the cornea equal to or less than
The rate at which energy is emitted, transferred, or received.
An enclosure that surrounds 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
The duration 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 (Hz).
A laser which delivers its energy in the form of a single pulse or a train of
pulses when the pulse duration is <0.25 s.
The variable aperture in the iris through which light travels to the interior of
A device for producing very short (~10-250
ns), intense laser pulses by enhancing the storage and dumping of electronic
energy in and out of the lasing medium, respectively.
A laser that emits short (~10-250
ns), high power pulses by means of a Q-switch.
A unit of angular measure equal to the angle subtended at the center of a circle
by an arc whose length is equal to the radius of the circle.
radians = 360 degrees.
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).
Energy emitted, transferred, or received in the form of radiation.
Surface density of the radiant energy received, expressed in units of
joules per centimeter squared (J x
Power emitted, transferred, or received in the form of radiation.
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 x sr-1).
Scattering of radiation in the course of its passage through a medium containing
particles whose sizes are small compared with the wavelength of the radiation.
The ratio of total reflected radiant power to total incident power.
Deviation of radiation following incidence on a surface.
The bending of a beam of light in
transmission through an interface between two dissimilar media or in a medium
whose refractive index is a continuous function of position (graded index
refractive index (index of refraction)
n, the ratio of the velocity of light in vacuum to the phase velocity in
repetitively pulsed laser (RPL)
A laser with multiple pulses of
radiant energy occurring in a sequence.
The sensory membrane which receives the incident image formed by the cornea and
lens of the human eye.
retinal hazard region
Optical radiation with wavelengths
between 0.4 mm
and 1.4 mm,
where the principal hazard is usually to the retina.
A mechanical device designed to slow direct entry to a controlled area.
A laser having a time-varying direction, origin, or pattern of propagation with
respect to a stationary frame of reference.
The rapid changes in irradiance levels in a cross-section of a laser beam due to
An enclosure to which casual access
is impeded by an appropriate means, e.g., a door secured by a magnetically or
electrically operated lock or latch, or by fasteners that need a tool to remove.
The viewing condition whereby the
angular subtense of the source,
amin, is equal to or less than the limiting
angular subtense, amin.
The three-dimensional angular spread at the vertex of a cone measured by the
area intercepted by the cone on a unit sphere whose center is the vertex of the
cone. Solid angle is expressed in
A laser or a laser-illuminated reflecting surface.
An individual who wishes to observe or watch a laser or laser system in
operation, and who may lack the appropriate laser safety training.
A mirror-like reflection.
Cloudiness in the connective tissue or main body of the cornea.
A stripping or peeling off of the surface layer of cells from the cornea.
A condition in which the combined effect is greater than the sum of the effects
of individual contributors.
The exposure duration (time) at which MPEs based upon thermal injury are
replaced by MPEs based upon photochemical injury to the retina
(limiting exposure duration)
For a pulsed laser, the duration for which the MPE is the same as the MPE for 1
ns. For thermal biological effects, this
corresponds to the ôthermal confinement durationö during which heat flow does
not significantly change the absorbed energy content of the thermal relaxation
volume of the irradiated tissue (Example: tmin is 18
ms in the spectral
region 0.4 to 1.05
mm and is 50
ms between 1.050
Passage of radiation through a medium.
The ratio of transmitted power to
Electromagnetic radiation with wavelengths shorter than those of visible
radiation; for the purpose of this standard, 0.18 to 0.4 mm.
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.
The unit of power or radiant flux.
The distance between two successive points on a periodic wave which have the