Nonlinear refractive indices of polystyrene films doped with azobenzene dye Disperse Red 1

Nonlinear refractive indices of polystyrene films containing azobenzene dye Disperse Red 1 (DR1) have been measured as a function of wavelength using the single beam Z-scan technique with a Fourier analysis of the transmittance time evolution. Although the C.W. excitation is carried out far from the absorption resonance region, the large nonlinear optical response has its origin in a thermal effect. We were able to find the thermal diffusivity coefficient of the sample.