Intrabeam viewing of extended-source lasers with telescopes

Magnifying optics can increase the hazards for intrabeam viewing of lasers. Although it is rather straightforward to evaluate these increased hazards for point-source lasers at distance, limited information is available for determining the hazards from viewing extended-source lasers from within the beam when magnifying optics are used. Since intrabeam viewing of nearly all lasers results in an extremely small retinal image, commonly known as a "point source," extended-source maximum permissible exposures (MPEs) are seldom applicable; however, a substantial correction factor is allowed for extended-source lasers in the determination of the MPE. In those rare cases where an extended-source laser is viewed by an optical aid, it is important to avoid applying an incorrect and sometimes very large extended-source correction factor. Extended-source lasers were constructed and then measured to determine if standard hazard classification techniques, mainly developed for point-source lasers, would adequately assess the true optical viewing hazards from viewing extended-source lasers with telescopes. It was found that current techniques are adequate since telescopes would normally be expected to be used at tens or hundreds of meters from the laser source, although purposeful exposure at close distance would require specialized hazard evaluation techniques.