Appendix 2 - Glossary of Terms

Accessible Exposure Limit (AEL) – The maximum accessible emission level permitted within a particular laser class.

Blink Reflex or Aversion Response  - The closure of the eyelid or movement of the head to avoid exposure to a noxious stimulant of bright light.  It generally occurs within 0.25 seconds, which includes the blink reflex time.

Continuous Wave (CW) -  The output of a laser, operated in a continuous rather than a pulsed mode.  For purposes of safety evaluation, a laser that is operated with a continuous output for a period of 0.25 seconds or greater 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 spatial distribution of a beam of radiation when it is reflected in many directions by a surface or by a medium.  Diffuse reflections are less hazardous than specular reflections for a given beam.

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).

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.

Environmental Health & Safety  - The department charged with implementing and maintaining the laser safety program at the University of Iowa.  The Laser Safety Officer is an EHS staff member and has the authority to enforce laser safety policies in order to effect the knowledgeable evaluation and control of laser hazards.

Infrared Radiation - Electromagnetic radiation with wavelengths that lie within a range of 700 nm to 1 mm.

Intrabeam Viewing - The viewing condition whereby the eye is exposed to all or part of a laser beam.

Irradiance (E) – Radiant power incident per unit area upon a surface, expressed in watts per square centimeter (W/cm2).

Laser -  A device that produces an intense, coherent, directional beam of light by stimulated emission of electronic or molecular transitions to lower energy levels. An acronym for Light Amplification by Stimulated Emission of Radiation.

Laser Operator -  An individual who has met all applicable laser safety training, medical surveillance, and approval requirements for operating a laser or laser system.

Maximum Permissible Exposure (MPE) -  The level of laser radiation to which a person may be exposed without hazardous effect or adverse biological changes to 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.

Optical Density (Di) -  Logarithm to the base ten of the reciprocal of the transmittance: Di = log T, where T is the transmittance.

Power -  The rate at which energy is emitted, transformed, or received in Watts/second or Joule/second. Also called the radiant power.

Principal Investigator -  The authorized laser user who assumes responsibility for the control and safe use of a laser or laser system.  

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 less than 0.25 seconds.

Q Switched Laser -  A laser that emits short (~30 nanoseconds), high-power pulses by means of a Q-switch.  A Q-switch produces very short, intense laser pulses by enhancing the storage and dumping of electronic energy in and out of the lasing medium, respectively.

Radiant Exposure (H) -  Surface density of the radiant energy received (Joules/cm2).

Radiant Flux (F) -  Power emitted, transferred, or received in the form of radiation, expressed in Watts (also called radiant power).

Repetitively Pulsed Laser -  A laser with multiple pulses of radiant energy occurring in sequence with a frequency of 1 Hz.

Specular Reflection -  A mirror-like reflection typically resulting from a shiny, flat surface. Specular reflections are more hazardous than diffuse reflections for a given beam.

Standard Operating Procedure (SOP) -  A set of operating instructions for a particular laser or laser system.  The procedure specifies measures which, if followed, will ensure safe and correct use of the laser or laser system.

Transmittance -  The ratio of total transmitted radiant power to the total incident radiant power.

Ultraviolet Radiation (Light) -  Electromagnetic radiation with wavelengths smaller than those of visible radiation; for the purpose of laser safety, 180 nm to 400 nm.

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 of 400 nm to 700 nm.

Watt – The unit of power or radiant flux.  1 watt = 1 Joule per second.

Wavelength  - The distance between two successive points on a periodic wave that have the same phase.