Characterization of thermo-optic nonlinearities in glass filters using the Z-scan technique

摘要

For nonlinear optical materials in which the excitation diffuses significantly during the time scale of measurement the usual analysis of a Z-scan experiment must be modified. We develop a simple first order theory based on a quadratic rather than Gaussian spatial modulation of the index of refraction. This leads to asymmetric Z-scan curves. We apply this theory to the study of the thermal-optic effect in a simple neutral density filter. A significant spatial phase chirp is can be induced in these filters at modest intensities. The observed transmission curves agree well with the quadratic theory