Effects of nonlinear Fabry-Perot resonator response on Z-scan measurements

We report experimental results of Z-scan investigations on the photoinduced nonlinear absorption and refractive index of submillimeter bulk samples of the III-V semiconductor InSb. The measurements were carried out in the cw regime at lambda = 10.6 mu m using a CO2 laser. The results put into evidence the contribution of the nonlinear Fabry-Perot resonator, constituted by the high-refractive-index sample itself, to the transmittance of the system. Such contribution can lead to a wrong evaluation of the nonlinear optical coefficents in Z-scan experiments. The experimental data were fitted using a modified Z-scan theory in which the effect of the resonator is taken into account. The values for the nonlinear absorption and refractive index used in the fit are in good agreement with those reported in literature.