Nonlinear absorption of CO 2 laser radiation by nonequilibrium carriers in germanium

Nonlinear absorption of CO ₂ laser pulses at the multi-MW level has been studied in n-type germanium at room temperature. This nonlinear absorption limits the level of CO ₂ laser intensity that can be transmitted through an optical grade germanium crystal. The observed nonlinearity may be interpreted in terms of nonequilibrium electron-hole pairs generated by hot electrons created by the intense laser field. The number of nonequilibrium carriers generated is measured by photoconductivity experiments, and the results are correlated to the absorption measurements.