Appendix F – Laser Safety Program Definitions
Accessible laser radiation: Laser radiation to which the human eye or skin may be
exposed for the condition (operation, maintenance or service) specified.
American National Standard for Safety Use of Lasers (ANSI Z136.1-2000):
Document that provides guidance for the safe use of lasers and laser systems by
defining control measures for each of four laser classifications.
Attenuation: The decrease in the radiant flux as it passes through an absorbing or
scattering medium.
Authorized personnel: Individuals approved by the Principal Investigator 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 or movement of the head to avoid an
exposure to a noxious stimulant or bright light. Aversion response to an exposure from
a bright laser source is assumed to occur with .25 s, including the blink reflex time.
Collateral radiation: Any electronic 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 or loupes.
Continuous wave (CW): The output of a laser that is operated in a continuous rather
than a pulsed mode. For purposes of safety evaluation, a laser operating with a
continuous output for a period > 0.25 s is regarded as a CW laser.
Controlled area: An area where the occupancy and activity of those within is subject to
control and supervision for the purpose of protection from laser radiation and related
hazards.
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.
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 the result of engineering features which limits the 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).
Failsafe 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.
Incident personnel: Individuals working in areas where there is a potential for
exposure to laser radiation from a Class 3B or Class 4 laser, but do not operate the
laser.
Infrared radiation: Electromagnetic radiation with wavelengths that lie within the range
0.7 µm to 1 mm.
Interlocks: An engineering control designed to prevent access to laser radiation above
the applicable maximum permissible exposure. The interlock may, for example, be
electrically or mechanically interfaced to a shutter that interrupts the beam when the
protective housing is opened or removed. Interlocks on protective housings that
enclose Class 3B or 4 lasers or laser systems are required. Remote interlocks for
rooms, entryways, or areas are recommended for Class 3B lasers or laser systems and
required for Class 4 lasers or laser systems.
Intrabeam viewing: The viewing condition whereby the eye is exposed to all or part of
a laser beam.
Laser: A device the produces radiant energy pre-dominantly by stimulated emission.
Laser radiation may be highly coherent temporally, or spatially, or both. An acronym for
Light Amplification by Stimlated Emission of Radiation.
Laser barrier: A device used to block or attenuate incident direct or 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 controlled area: See Controlled Area.
Laser operator: See Authorized Personnel.
Laser Safety Officer (LSO): One who has the 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 one or more lasers.
Maintenance: 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.
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. MPE is expressed in terms of either radiant exposure (joules/cm2) or
irradiance (watts/cm2). The criteria for MPE are detailed in Section 8 of ANSI Z136.1.
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.)
Non-beam Hazard: A class of hazards that result from factors other than direct human
exposure to a laser beam.
Operation: The performance of the laser or laser system over the full range of its
intended functions (normal operation).
Optical density: Logarithm to the base ten of the reciprocal of the transmittance. The
higher the optical density, the lower the transmittance.
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.
Pulsed laser: A laser that delivers its energy in the form of a single pulse or a train of
pulses. The duration of a pulse is regarded to be < 0.25 s.
Q-switch: 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.
Repetitive pulse laser: A laser with multiple pulses of radiant energy occurring in
sequence.
Reversible bleaching: The absorbing filter of laser eyewear may become temporarily
saturated from an ultrashort laser pulse, causing the beam to pass through.
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. These are usually performed by qualified technical personnel
provided by the manufacturer or other service companies.
Specular reflection: A mirror-like reflection.
Ultraviolet radiation: Electromagnetic radiation with wavelengths smaller than those
of visible radiation; for the purpose of this manual, 0.18 to 0.4 µm.
Visible radiation (light): 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 to
0.7 µm.
Wavelength: The distance between two successive points on a periodic wave which
have the same phase.