Laser Safety Classification

Class 1: A Class 1 laser is considered safe based upon current medical knowledge. This class includes all lasers or laser systems which cannot emit levels of optical radiation above the exposure limits for the eye under any conditions inherent in the design of the laser product. There may be a more hazardous laser embedded in the enclosure of a Class 1 product, but no harmful radiation can escape the enclosure.Class 2: A Class 2 laser or laser system must emit a visible laser beam. Class 2 laser light is too dazzling to stare into for extended periods. Momentary viewing is not considered hazardous since the upper radiant power limit on this type of device is less than the Maximum Permissible Exposure for momentary exposure of 0.25 seconds or less. Intention extended viewing, however, is considered hazardous. Class 3: A Class 3 laser or laser system can emit any wavelength, but it cannot produce a diffuse (not mirror-like) reflection hazard unless focused or viewed for extended periods at close range. It is also not considered a fire hazard or serious skin hazard. Any continuous wave (CW) laser that is not Class 1 or Class 2 is a Class 3 device if its output power is 0.5 W or less. Since the output beam of such a laser is definitely hazardous for intra-beam viewing, control measures center on eliminating this possibility.Class 4: A Class 4 laser or laser system is any that exceed the output limits (Accessible Emissions Limits, AELs) of a Class 3 device. As would be expected, these laser may be either a fire or skin hazard or a diffuse reflection hazard. Very stringent control measures are required for a Class 4 laser or laser system. Ultrafast lasers fall into this classification.
Ultrafast lasers possess safety hazards not associated with light from conventional sources. Among potential injuries, eyes are the most vulnerable. Damage to the retina cannot be repaired and does not heal by itself.Why is eye safety so critical? Compare the output of femtosecond lasers with the radiation that the human eye can receive from the sun on a clear day. The sun’s image on the retina is approximately 160 microns. This yields a radiation density of around 30 W/cm2. A typical Ti:Sapphire femtosecond oscillator is capable of producing intensity in excess of 50 GW/cm2, while an amplifier will easily exceed 1014 W/cm2. Obviously, very weak laser reflections, or even scattering from rough surfaces, can be extremely bright - dangerously bright - to the eyes.You are urged to read carefully the safety section found in the user manual of any laser product you use and to strictly adhere to those instructions.