Dispersion of the Nonlinear Optical Susceptibility inn−InSb

Using a C${\mathrm{O}}_2$ laser, we have observed the dispersive behavior of the third-order nonlinear optical susceptibility, ${\chi }^{\mathrm{}\left(3\right)\mathrm{}}(-{\omega }_3,{\omega }_1,{\omega }_1,-{\omega }_2)$, in $n-\mathrm{I}\mathrm{n}\mathrm{S}\mathrm{b}$ in a magnetic field. The resonances occur when the difference frequency ${\omega }_2-{\omega }_1$ is near the cyclotron frequency, or twice the cyclotron frequency. A connection is drawn between the dispersion of ${\chi }^{\mathrm{}\left(3\right)\mathrm{}}$ and the spontaneous and stimulated Raman scattering from Landau levels. A simple semiclassical theory shows the correct polarization properties and resonance behavior of ${\chi }^{\mathrm{}\left(3\right)\mathrm{}}$ and is qualitatively in agreement with experiment.