Issues and Future Directions

The investigation performed by Kwak et al. [346] demonstrated that amorphous chalcogenide thin films, including As₂S₃ films, offer promise as materials for optical limiters. The optical-limiting effects are of special interest in nonlinear optics and optoelectronics owing to their possible application for the protection of eyes and sensitive detectors against intense radiation. The mechanisms responsible for optical limiting are of different nature. Reverse saturable absorption, which is associated with a large cross-section of absorption from excited levels, brings about optical-limiting effects in colloidal metals [347], fullerenes [348], and phthalocyanines [349]. The optical limiting in organic clusters is caused by strong nonlinear refraction [350], whereas the optical limiting in semiconductor structures is governed by two-photon absorption (2PA) [351].