Computation of effective source size for extended sources

A laser hazard evaluation compares the potential laser exposure to the maximum permissible exposure (MPE). Direct intrabeam viewing of a collimated laser beam produces a minimally sized retinal image. Viewing other laser sources often produces a larger retinal image known as an extended source. An optical limiter is designed to protect the eye from direct laser exposure through a combination of absorption and scattering, producing an extended source. Diode lasers in combination with diffusers also produce extended sources when viewed at a close distance. A substantial increase in the MPE is allowed for extended sources, based on the size of the retinal image. The larger retinal image produced by the optical limiter does not exhibit a Gaussian or top-hat profile, making it often difficult to judge its effectiveness. Therefore, it is necessary to define methods to quantify the reduction in hazard. The partial areas method that is currently used overestimates the reduction in hazard from a single extended source with a strong central peak.