Optical bistability in InSb at room temperature with two‐photon excitation

We report the observation of optical bistability in an InSb resonator at room temperature. This effect and fringe shifts were caused by nonlinear refraction induced by two‐photon absorption of radiation from a single longitudinal mode injection‐locked pulsed CO2 laser operating at 9.6–10.6 μm. Intensities as low as 100 kW/cm2 were found to be sufficient to tune the 250‐μm‐thick cavity through a fringe maximum. From our results we deduce a value of χ(3) of the order of 10−4 esu over the range of intensities investigated