Dispersion of the Lowest-Order Optical Nonlinearity in InSb

Second-harmonic generation has been studied in InSb. The fundamental source was a ${\mathrm{CO}}_2$ laser, and the second-harmonic photon energies were near the band edge. The non-linear susceptibility $d_{14}$ is the largest known and shows significant frequency dependence. In a 2.6% range of photon energies, $\left|d_{14}\right|$ changes by 31% while the linear susceptibility at the second harmonic, ${\chi }^{\mathrm{lin}}\left(2\mathrm{}\omega \right)$, changes by only 2.8%. In addition $d_{14}=\left|d_{14}\right|e^{i\varphi }$ is complex with $\varphi \cong -50\mathrm{}°$.