Optical hysteresis and light absorption in a-As2S3 and c-As2S3

Results of the experimental investigations of nonlinear absorption of laser pulses in amorphous a-As₂S₃ films are presented. The optical transmission hysteresis and reversible film photodarkening at interband excitation of a-As₂S₃ films in a blue-green spectral region is reported for the first time. It was suggested that the nonlinear light absorption could be explained by taking into account the light interaction with nonequilibrium localized lattice vibrations anharmonically coupled with the extended phonons. The measurements of peculiarities of the pulse absorption in crystalline c-As₂S₃ films can confirm the proposed explanation