Resonant Optical Nonlinearity Due to Conduction-Electron Spins in InSb

Second-order resonant optical nonlinearity due to conduction-electron spins has been observed by difference-frequency generation of far-infrared radiation (90.1 ${\mathrm{cm}}^{-1\mathrm{}}$) in $n-\mathrm{I}\mathrm{n}\mathrm{S}\mathrm{b}$ at 15°K $n=2.2\mathrm{}\times {10}^{15}$ ${\mathrm{cm}}^{-3\mathrm{}}$). When the spin-resonance frequency is tuned to the difference frequency, the measured effective nonlinear coefficient for a linewidth of 114 G is 5.4 times larger than the conventional second-order nonlinear coefficient $d_{14}$.