HAZARDS WITH LASER
It seems appropriate to mention at this point some appraisal of the hazards of experimenting with lasers. Several local burns can be caused when the laser beam is focuses on any part of the body, and burns of lesser consequence may be caused even by unfocused beams from very powerful lasers. The primary danger is , of course, to the eye because it automatically focuses the incident radiation on the retina. Obviously one must under all circumstances avoid looking directly into the laser when there is a possibility that it may be fired. The pulsed laser is most dangerous because all its energy is delivered in a much shorter time than it takes to close the eyelid. Since a minute fraction of the normal pulse energy is sufficient to damage the eye, one should avoid the possibilities that spectral reflection from a metal or glass surface reaches an observer's eye. The beam may be observed on a matte white screen. The primary danger with a continuously operating laser is from the infrared coherent radiation and from the incoherent ultraviolet radiation which may be emitted by the discharge used for excitation. The experimenter may not be immediately aware of the presence of these radiation. In any case, laser beam is not the only hazard. A careless experimenter may be electrocuted by the power supply before he becomes blinded by the beam.
Since the energy output of pulsed lasers varies from about 0.1 joule to 1000 joules and the collimation of the output beams is also highly variable, it not practical to state quantitative safety rules applicable in every case. The precautions must be appropriate to the total energy concentration available under given circumstances. The basic concept of the universal classification schemes is as follows considering the exposure limit is averaged over a 7 mm aperture:
- Class I : Class I laser products are essentially safe and are typically enclosed systems which do not emit hazardous level.
- Class II : Class II laser products are limited to visible lasers that are safe for momentary viewing but should not be stared at continuously unless the exposure is within the recommended ocular limits.
- Class III: Class III laser products are not safe even for momentary viewing, and procedural controls and protective equipment are normally required for their use.
Class IV: Class IV laser products are normally considered more hazardous than class III devices since they may represent a significant fire hazard or skin hazard and may also produce hazardous diffuse reflection.
The laser laboratory should be brightly illuminated. Raising the ambient light level results in contracting the eye pupil there by lesser laser energy reaches the retina. All optical arrangements/layouts should be so configured that the direct laser beam does not rise to the eye-level, and wherever possible, backstops should be positioned to block the laser beam. The laser laboratory should have a caution mark EYE HAZARD AREA displayed prominently.
 
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