We describe a completely passive technique for limiting the power of light beams. The techniques we use are based on optical self-action (self-focusing or defocusing) and non-linear absorption or a combination of both. These processes are passive and thus require no external mechanism to induce limiting other than the light beam itself.
M. J. Soileau,
Eric W. Van Stryland,
"Passive Optical Limiting", Proc. SPIE 0540, Southwest Conf on Optics '85, (20 November 1985); doi: 10.1117/12.976084; https://doi.org/10.1117/12.976084