The acronym LASER stands for Light Amplification by Stimulated Emission of Radiation. A laser is a device which when energized can emit a highly collimated coherent beam of intense monochromatic electromagnetic radiation. This radiation can be emitted over a wide range of the electromagnetic spectrum from the ultraviolet region through the visible to the infrared region. The range of commonly available lasers is from 200 nanometers to 10.6 micrometers. These emissions may be in either continuous or pulse form depending on the laser system.
Since laser operations normally fall outside of the wavelengths required to produce ionizing radiation, the primary mechanism of beam damage is thermal. However, it should be noted that photochemical damage might occur while dealing with lasers operating in the ultraviolet region. The irradiance and the associated potential hazards depend upon the type of laser, beam characteristics, and the application of the laser system.
Common Laser Wavelengths
Spectral Region
Medium
Wavelength (nm)
Ultraviolet (180–400)
Argon Fluoride (ArF)
193
Krypton Chloride (KrCl)
222
Krypton Fluoride (KrF)
248
Xenon Chloride (XeCl2)
308
Nitrogen (N2)
337
Helium-Cadmium (HeCd)
325
Visible (400-700)
Argon (Ar)
488-515
Copper Vapor (CVL)
511, 578
Helium-Neon (HeNe)
543; 594; 612; 633
Krypton (Kr)
647
Ruby
694
Infrared (700-1000)
Titanium-Sapphire (Ti:Al2O3)
650-1100
Gallium-Arsenide (GaAs)
850
Neodymium-YAG (Nd:YAG)
1,064
Holmium-YAG (Ho:YAG)
2,100
Carbon Dioxide (CO2)
10,600
Laser Classifications
The American National Standards Institute (ANSI) has established a laser hazard classification system in publication, ANSI Z136.l-2007. The objective of the system is to provide reasonable and adequate guidance for the safe use of lasers and laser systems. Laser manufacturers are required to label all laser products, excluding Class 1, with appropriate class and beam characteristic information.
Note:Any class laser system could potentially have an embedded laser of a higher class inside of it that may be accessible during maintenance or repair.
The following is a summary of the ANSI classification scheme and the hazard(s) associated with each class of laser:
Class 1 laser system
Considered to be incapable of producing damaging radiation levels during operation “Eye Safe”, and
Exempt from any control measures or other forms of surveillance.
Note:Items previously classified as Class IIa under the Federal Laser Product Performance Standard (FLPPS) should be treated the same as Class 1.
Class 1M laser system
Considered to be incapable of producing hazardous exposure conditions during normal operation unless the beam is viewed with an optical instrument such as an eye-loupe (diverging beam) or a telescope (collimated beam), and
Exempt from any control measures or other forms of surveillance other than to prevent potentially hazardous optically aided viewing.
Class 2 laser system
Emits in the visible portion of the spectrum (400-700 nm), and
Eye protection is normally afforded by the “aversion response”, <.25 seconds.
Class 2M laser system
Emits in the visible portion of the spectrum (400-700 nm),
Eye protection is normally afforded by the “aversion response” for unaided viewing; and
Potentially hazardous if viewed with optical instrument such as an eye- loupe (diverging beam) or a telescope (collimated beam).
Class 3R laser system
Is potentially hazardous under direct and specular reflection viewing conditions if the eye is appropriately focused and stable,
Does not pose a diffuse reflection hazard, and
Does not pose a fire hazard.
Class 3b laser system
May be hazardous under direct and specular reflection viewing conditions,
Is normally not a diffuse reflection or fire hazard,
Requires laser safety PPE and controls (Interlocks are required to be connected to laser in use signage for all Class 3b and 4 laser systems installed or modified after 2012.), and
Barriers, shields, and curtains may be recommended by the LSO and/or LSS when deemed appropriate following a hazard evaluation.
Note:Formerly labeled Class IIIa lasers with a “Danger” logo have been reclassified as 3R.
Class 4 laser system
Is a hazard to the eye and skin from specular reflection and intrabeam exposures under all conditions,
Is a fire hazard,
May produce laser generated air contaminants (LGAC),
May produce plasma (UV) radiation,
Requires laser safety PPE and controls (Interlocks are required to be connected to laser in use signage for all Class 3b and 4 laser systems installed or modified after 2012.), and
Barriers, shields, and curtains may be recommended by the LSO and/or LSS when deemed appropriate following a hazard evaluation.
Note:During maintenance and service the classification associated with the maximum level of accessible laser radiation shall be used to determine the applicable control measures.
Since laser pointers are the most commonly used laser devices considerations should be observed when using these devices regardless of the classification. Please see appendix: BU- 02 (Laser Pointer Guidance) for additional information.
Categories of Active Laser Medium
One way to characterize lasers is by their active medium. Each medium exhibits it own unique set of advantages as well as challenges with regard to the amount of energy that can be stored, ease of handling and storage, secondary safety hazards, cooling properties, and physical characteristics of the laser output. Common gain mediums include crystals, glasses, gases, semiconductors, and liquids.
Solid-State
The term “solid state”, as related to lasers, refers to a group of optically “clear” materials such as glass or a “host” crystal with an impurity dopant. In this group, the host material is chosen for its optical, mechanical, and thermal properties. While the dopant is selected for its ability to form a population inversion and emit laser light, the material determines the output wavelength.
The most common example of this group are the Nd(III):YAG (Neodymium: Yttrium/Aluminum/Garnet) lasers, where neodymium ions are the impurity in the solid crystalline host material known as “YAG”. These lasers are often high powered and pumped by a flashtube or laser diodes.
Also very common in this group are the Ti:Saphire (Ti:Al2O3) lasers, where the titanium ions are the impurity in a Sapphire crystal. Like the Nd:YAG lasers, Ti: a secondary laser such as an Argon-Ion often pumps Sapphire lasers or frequency doubled Nd:YAG. These lasers are often high powered and tunable in nature and can be operated in either the continuous wave (CW) or pulsed modes.
Semiconductor (Diode)
Diode lasers are the most numerous lasers currently in use. The two common families of diode lasers are composed of GaAlAs (Gallium/Aluminum/Arsenide), with output wavelengths in the 750 to 950 nm (commonly used in CD and CD/ROM players), and InGaAsP (Indium/Gallium/Arsenide/Phosphide), which has a wavelength in the 1100- 1650 nm range (used in optical telecommunications).
Semiconductor lasers are commonly seen in research environments in conjunction with higher-powered solid-state lasers as a pump or as semiconductor arrays.
Liquid (Dye)
Liquid lasers utilize a flowing dye as the active medium, and are pumped by a flash lamp or by another laser, such as an Argon-Ion laser. Dye lasers are typically complex systems requiring more maintenance and upkeep. They are operated in either pulsed or continuous wave mode depending largely on pumping configuration. One advantage of dye lasers is that dyes are wavelength tunable over a range of approximately 100 nanometers each. Common availability of dye types yields sub 400 nanometers to over 850 nanometers tunability ranges.
Gas
Gas laser systems utilize a gas, or gas mixture, confined to a tube. An electric current passes through the tube exciting the atoms and causing them to emit light. Mirrors at the ends of the tubes form a resonant cavity and primarily determines the laser wavelength.
Gas laser systems use different gas mixtures and solid particles to produce variety wavelengths. Common examples of these gas systems are the Carbon Dioxide (CO2) and Argon-Ion (Ar) laser types. A sub-category of this grouping is known as the Excimer lasers (“excited dimer”), such as the Xenon-Chloride (XeCl) laser. Excimer lasers operate in the ultraviolet region of and poses acute chemical hazards that must be accounted for.