Optical Nonlinearities due to Mobile Carriers in Semiconductors

Optical nonlinearities due to conduction-band electrons have been observed in InAs, InSb, GaAs, and PbTe using 10.6-\ensuremath{\mu} (${\ensuremath{\omega}}_{1}$) and 9.6-\ensuremath{\mu} (${\ensuremath{\omega}}_{2}$) radiation from a $Q$-switched C${\mathrm{O}}_{2}$ laser. Difference frequencies ${\ensuremath{\omega}}_{3}=2{\ensuremath{\omega}}_{1}\ensuremath{-}{\ensuremath{\omega}}_{2}$ at 11.8 \ensuremath{\mu} and ${\ensuremath{\omega}}_{4}=2{\ensuremath{\omega}}_{2}\ensuremath{-}{\ensuremath{\omega}}_{1}$ at 8.7 \ensuremath{\mu} were measured for a variety of carrier concentrations at several temperatures.