Third-order optical nonlinearities of silver doped and/or silver-halide modified Ge-Ga-S glasses

The third-order optical nonlinearities of silver doped and/or silver-halide (AgX, X = Cl, Br, I) modified Ge-Ga-S sulfide glasses are studied by the femtosecond Z-scan method. A general agreement with empirical rules is reached: the nonlinear refractive index scales with the optical bandgap or Sellmeier gap of the samples. However, the AgI-modified glass having a larger linear refractive index than that of AgCl-modified one, exhibits a smaller nonlinear refractive index, in contrary to Miller's rule. This has been explained based on the analysis of the structure of the samples.