Laser irradiation induced enhancement on the ultrafast third-order optical nonlinearity of chalcogenide glass

The third-order optical nonlinearity of chalcogenide glass was investigated with the femtosecond optical Kerr gate system. With the long durative irradiation of the laser field, the ultrafast optical Kerr signal was observed to increase continuously till saturation. It was also found that this enhancement is anisotropic with respect to the laser polarization. Based on the intimate valence alteration pairs (IVAP) model, we explained this enhancement in terms of the light-induced orientation of valence alteration pairs.