US Laser Safety Standards
|1||Non-hazardous||Eyewear not required.|
|1M||Eye safe visible laser (400-700nm) if used without magnifying optics.||Eyewear not required unless used with magnifying optics.|
|2||Eye safe visible laser (400-700nm) (safe within the blink reflex of 0.25s).||Eyewear not required.|
|2M||Eye safe visible laser (400-700nm) (safe within the blink reflex of 0.25s) if used without magnifying optics.||Eyewear recommended.|
|3R||Likely unsafe for intrabeam viewing. Maximum Permissible Exposure (MPE) is up to 5 times class 2 limit for visible lasers of 5 times class 1 limit for invisible lasers.||Eye hazard; eyewear is recommended.|
|3B||Eye hazardous for intrabeam viewing. Limited diffuse hazard.||Eye hazard; eyewear is recommended.|
|4||Eye and skin hazard for direct and diffuse exposure. Fire and burn hazard.||Eye protection and other personal safety equipment is required.|
ANSI Z136.1 requires specification of laser safety eyewear according to optical densities (OD), and allows a Nominal Hazard Zone (NHZ) to be calculated, outside which diffuse viewing eyewear is allowed.
Optical Density (OD) is a measure of the attenuation of energy passing through a filter. The higher the OD value, the higher the attenuation and the greater the protection level. In other words, OD is a measure of the laser energy that will pass through a filter.
OD is the logarithmic reciprocal of transmittance, expressed by the following:
D? = -log10 T ? (where T is transmittance)
|OD (Optical Density)||Transmission in %||Attenuation Factor|
Modes of Operation
Lasers operating at different modes have different power density characteristics and often different eyewear requirements.
|D||Continuous Wave (cw) with consistent average power||greater than 0.25 second|
|I||Pulsed: short single or periodic energy emission||> 1 µs to 0.25 s|
|R||Giant Pulsed: very short single or periodic energy emission||1 µs to 1 ns|
|M||Mode Locked||< 1 ns (pico and femtosecond)|