Power/energy limiter using reverse saturable absorption

In materials with an excited-state absorption cross section larger than the ground-state absorption cross section, increasing the incident light intensity (thus populating the excited state) increases the absorption. We show that such a reverse saturable absorber can function as a power limiter and pulse smoother for long pulses and as an energy limiter and pulse shortener for short pulses. The necessary properties for such a material are described. Reverse saturable absorption is demonstrated at 488 nm in alexandrite. A simple model describing these effects is presented.