Optical nonlinearities of PbSe are studied in picosecond pumphyphen;probe experiments at wavelengths from 4 to 8 mgr;m. Excitation of an electronhyphen;hole plasma leads to a shift of the absorption edge to higher energies and to large changes of the refractive index by up to minus;0.1 for a carrier density of 4times;1017cmminus;3. The optical nonlinearities result from band filling by both electrons and holes. The timehyphen;dependent absorption change shows a partial recovery within 100 ps, giving evidence of enhanced recombination rates. Theoretical calculations of the absorption change are in agreement with the experimental data.
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