Another look at saturable absorbers for laser eye protection

Abstract
A number of approaches are being explored to provide eye protection against visible wavelength lasers while maintaining adequate transirtission for visual performance. Real protection at this time is provided by fixed wavelength reflectors and absorbers and if a plastic substrate is required only absorbers have been reliably produced. An absorber useful in the visible spectruit must have a very narrow absorption band centered at the appropriate laser wavelength with minimum attenuation outside that band. With such restrictions the choice of absorbers is liirited and many of the choices that do exist are saturable absorbers. A saturable absorber becomes increasingly transparent to an incident laser beam as the irradiance of that beam increases thus it would seem to be a poor choice for ocular protection. Nevertheless for some wavelengths saturable absorbers are the only absorbers available. We have performed some tests with a phthalocyanine dye in a plastic substrate to explore limits within which a saturable absorber can be used without comproruising eye safety. 1