Simultaneous measurements of thermally induced birefringence and thermal refraction in absorptive glass filters

A polarization-analysed z-scan experiment is used to characterize the therm al nonlinear refraction, thermal birefringence and optical limiting induced by a moderate-power continuous-wave laser in absorptive neutral-density fi lters. Strong thermal nonlinear refraction is observed, corresponding to a nonlinear quadratic phase shift of the order of unity at modest powers of a few hundred milliwatts. We are able to qualitatively describe the main obs erved dependences of these interrelated phenomena through a simple theoreti cal model that invokes a quadratic spatial profile for the temperature incr ease induced by the incident radiation within the filters.