Index of refraction modifications accompanying absorptive optical bistability in a semiconductor doped glass filter

We have characterized the transverse spatial dependence of the real and imaginary parts of the complex nonlinear refractive index of a semiconductor doped glass filter, which exhibits absorptive bistability. Using the Z-scan technique, combined with an interferometric measurement of the integrated optical thickness, we are able to fit the observed experimental data assuming a quadratically varying transverse temperature profile in the sample. The transverse variations in the nonlinear refractive index do not scale directly with the size of the incident beam, but exhibit marked asymmetries depending on whether the incident beam is converging or diverging.