Optical nonlinearities due to conduction-band electrons have been observed in InAs, InSb, GaAs, and PbTe using 10.6-μ (${\omega }_1$) and 9.6-μ (${\omega }_2$) radiation from a $Q$-switched C${\mathrm{O}}_2$ laser. Difference frequencies ${\omega }_3=2\mathrm{}{\omega }_1-{\omega }_2$ at 11.8 μ and ${\omega }_4=2\mathrm{}{\omega }_2-{\omega }_1$ at 8.7 μ were measured for a variety of carrier concentrations at several temperatures.

• Received 4 October 1966

DOI:https://doi.org/10.1103/PhysRevLett.17.1011