Spectral and temperature dependence of two-photon and free-carrier absorption in InSb

Abstract

The nonlinear absorption spectrum of InSb was measured using a combination of tunable $\ensuremath{\sim}160\text{ }\text{fs}$, $\ensuremath{\sim}10\text{ }\text{ps}$, and $\ensuremath{\sim}150\text{ }\text{ns}$ IR sources along with a cryostat for controlling the sample temperature to vary the band gap energy from 0.17 to 0.23 eV. The measured nonlinear optical properties in InSb are consistent with those predicted by the models which include two- and three-photon absorption (2PA and 3PA), multiphoton generated free-carrier absorption (FCA) and various recombination mechanisms. Temperature-dependent Z-scan and nonlinear transmission measurements yield information on the temperature and spectral dependence of 2PA, FCA, and carrier recombination processes of Shockley-Read-Hall, and Auger mechanisms. We find good agreement between the measured and the modeled nonlinear properties is possible only when the recently predicted temperature dependence of the FCA is considered. The wavelength- and temperature-dependent 2PA and 3PA coefficients in InSb were experimentally obtained. The inferred values of the 2PA and 3PA are consistent with the scaling rules of a simple two-parabolic band model. We further determine recombination rates from nonlinear transmittance of nanosecond pulses of ${\text{CO}}_{2}$ laser.