Calculated temperature rise in midinfrared laser irradiated Hg0.72Cd0.28Te

Abstract

We present results from a numerical study on heating in a 10μm thick layer of Hg0.72Cd0.28Te induced by 1μs long laser pulses at photon energies close to the band gap of the material. A number of highly nonlinear mechanisms contribute to the heating, their relative importance being dependent on laser wavelength, instantaneous irradiance, and material temperature. Mechanisms studied include one- and two-photon absorptions across the band gap, intervalence band absorption between light- and heavy hole bands, electron-hole recombination, free-carrier absorption, excess carrier temperatures, and refractive index changes. The increase in band gap with temperature eventually terminates one-photon absorption from the valence to the conduction band, and further heating is driven by much weaker absorption processes. The varying band gap also introduces changes in electron- and light hole masses and thereby in the separation between the light- and heavy hole bands, thus strongly affecting intervalence band absorption. At the shortest laser wavelength of 3.8μm, the simulations indicate that surface melting will occur at fluence levels in the range of 2–3J∕cm2, while more than 10J∕cm2 will be required for melting at wavelengths beyond 5μm.