Large nonlinear refraction in InSb at 10 μm and the effects of Auger recombination

Narrow bandgap semiconductors exhibit very large optical nonlinearities in the infrared owing to large two-photon absorption that scales as the inverse cube of the bandgap energy and the large losses and refraction from two-photon generated free carriers. Except for extremely short pulses, the free-carrier effects dominate the nonlinear losses and nonlinear refraction. Here we develop a method for the calculation of the free-electron refraction cross section in InSb. We also calculate the Auger recombination coefficient in InSb and find it to be in good agreement with existing experimental data. In all the calculations we rely on Fermi-Dirac statistics and use a four-band k⋅p theory for band structure calculations. Experiments on the transmission of submicrosecond CO2 laser pulses through InSb produce results consistent with the calculated parameters.