The Helium-Neon laser used in the Optics Laboratory produces an intense beam of light. The power level of the laser used in the Optics Laboratory is approximately 1.5 mW. This is a low-power laser. The beam will not harm the skin, even upon direct exposure. The human eye, however, is much more susceptible to injury by laser light. The lens of the eye focuses the beam to a very small spot on the retina, the light sensitive layer at the back of the eye. The resulting high intensity may lead to a local burn, which may cause degradation of vision, depending on the exact location and size of the spot.
The components of the eye are vulnerable to different wavelengths of electromagnetic radiation. Each wavelength region must be considered separately when evaluating the potential hazards. The far ultraviolet and the far infrared wavelengths are entirely absorbed by the cornea and the lens. Near ultraviolet light is partially absorbed in the cornea, lens and the retina, and can damage all three. Light with visible or near infrared wavelengths poses the greatest danger to the retina because the lens focuses these wavelengths on the retina.
Tissue damage by heating occurs when the heat energy deposited by light exceeds the capacity of the tissues to safely carry the heat away. Lasers hazards are characterized by Classes. The class of a laser depends on the laser power and on the emission wavelength. The Class of a laser is defined by the American National Standards Institute (ANSI) according to the degree of hazard presented.
CLASS I LASERS: Class I lasers are low-powered and do not emit hazardous radiation under normal operating conditions because they are completely enclosed. Class I lasers are exempt from any control measures. Equipment, such as laser printers and laser disc players, are examples of this class.
CLASS II LASERS: Class II lasers emit accessible visible laser light with power levels less than 1 mW radiant power and are capable of creating eye damage through chronic exposure. The human eye blink reflex, which occurs within 0.25 seconds of exposure to the Class II laser beam, provides adequate protection. It is possible to overcome the blink response and stare into the Class II laser long enough to damage the eye. Class II lasers are exempt from any control measures. Equipment, such as some visible continuous wave Helium-Neon lasers and some laser pointers, are examples of Class II lasers.
CLASS IIa LASERS: Class IIa lasers are special purpose lasers that emit accessible visible laser light with power levels less than 1 mW radiant power and are not intended for viewing. This class of lasers causes injury when viewed directly for more than 1,000 seconds. Class IIa lasers are exempt from any control measures. Equipment, such as some bar code readers, are examples of Class IIa lasers.
CLASS IIIa LASERS: Class IIIa lasers are systems with power levels of 1 to 5 mW that normally would not produce a hazard if viewed for only momentary periods with the unaided eye. They pose severe eye hazards when viewed through optical instruments (e.g., microscopes, binoculars, or other collecting optics). Class IIIa lasers must be labeled. A warning label shall be placed on or near the laser in a conspicuous location and caution users to avoid staring into the beam or directing the beam toward the eye of individuals. Equipment, such as some visible continuous wave Helium-Neon lasers and some solid state laser pointers, are examples of Class IIIa lasers.
CLASS IIIb LASERS: Class IIIb lasers are systems with power levels of 5 mW to 500 mW for continuous wave lasers or less than 10 J/cm² for a 0.25 s pulsed laser. These lasers will produce an eye hazard if viewed directly. This includes intrabeam viewing or specular reflections. Higher power lasers in this class will also produce hazardous diffuse reflections. Specific control measures covered in Class IIIb lasers shall be used in areas where entry by unauthorized personnel can be controlled. Entry into the area by personnel untrained in laser safety may be permitted by the laser operator if instructed in applicable safety requirements prior to entry and provided with required protective eye wear.
CLASS IV LASERS: Class IV lasers are systems with power levels greater than 500 mW for continuous wave lasers or greater than 10 J/cm² for a 0.25 s pulsed laser. These lasers will produce eye, skin and fire hazards. This includes intrabeam viewing, specular reflections or diffuse reflections.
EMBEDDED LASERS: Embedded lasers are found in laser products with lower class ratings. Laser printers, CD players, and laser welders may have Class III or Class IV lasers in their protective and interlocked housings. When such a laser system is used as intended, the lower laser class applies. When such a system is opened (e.g., for service or alignment) and the embedded laser beam is accessible, the requirements for the higher class of the embedded laser must be implemented.
Follow these guidelines at all times to insure the safety of yourself and others working in the Optics Laboratory .