Two-photon absorption coefficients β2 of eight different semiconductors with bandgap energy Eg varying between 1.4 and 3.7 eV are measured using 1.06 μm and 0.53 μm picosecond pulses. β2 is found to scale as E−3g as predicted by theory for the samples measured. Extension of the empirical relationship between β2 and Eg to InSb with Eg = 0.2 eV also provides agreement between previously measured values and the predicted β2. In addition the absolute values of β2 are in excellent agreement (the average difference being >26%) with recent theory which includes the effects of nonparabolic bands. The nonlinear refraction induced in these materials is monitored and found to agree well with the assumption that the self-refraction originates from the two-photon generated free carriers. The observed self-defocusing yields an effective nonlinear index as much as two orders of magnitude larger than CS2 for comparable irradiances. This self-defocusing in conjunction with two-photon absorption is used to construct a simple, effective optical limiter that has high transmission at low input irradiance and low transmission at high input irradiance. The device is the optical analog of a Zener diode.

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