Nonlinear Optical Susceptibilities from Electroreflectance Moments Analysis

The first moments of a series of Kramers-Kronig-transformed experimental electro-reflectance spectra are calculated in order to estimate critical-point contributions to the second- and third-order nonlinear optical susceptibilities, ${\chi }^{\mathrm{}\left(2\right)\mathrm{}}$ and ${\chi }^{\mathrm{}\left(3\right)\mathrm{}}$. Analysis of data for Ge and GaAs provides the first direct experimental evidence that the electronic resonant processes responsible for electroreflectance contribute negligibly to ${\chi }^{\mathrm{}\left(2\right)\mathrm{}}$, but significantly affect the value of ${\chi }^{\mathrm{}\left(3\right)\mathrm{}}$.