Large and opposite changes of the third-order optical nonlinearities of chalcogenide glasses by femtosecond and continuous-wave laser irradiation

We report that the nonlinear refractive index (n2) of As2S3 glass can be enhanced after irradiation by a femtosecond laser but suppressed after irradiation by a continuous-wave (cw) laser, although both the femtosecond laser and cw laser induce photodarkening in the glass. Photodarkening by the femtosecond laser increases n2 by as much as 50%, while irradiation by a subbandgap cw laser decreases n2 by as much as 60% of its original value. The results provide a way to manipulate the third-order optical nonlinearity of this photonic glass. Mechanisms of the optical nonlinearity changes are discussed.