Hyper-Raman scattering from alkali halides

Hyper-Raman spectra of five alkali halides (NaCl, KCl, KBr, KI, and RbI) have been measured at room temperature. The results are compared in detail with infrared data. Satisfactory agreement is found. The hyper-Raman line shapes are shown to provide a sensitive test for theoretical calculations of the complex frequency-dependent self-energy function. We estimate the absolute hyper-Raman scattering efficiency by relating the electro-optic coupling coefficients to the nonlinear third-order susceptibility known from the literature. We obtain scattering efficiencies between ${10}^{\mathrm{-}18}$ and ${10}^{\mathrm{-}15}$ ${\mathrm{cm}}^{\mathrm{-}1}$ ${\mathrm{sr}}^{\mathrm{-}1}$ for a laser intensity of 100 MW/${\mathrm{cm}}^2$. We also measure the relative values of all hyper-Raman tensor elements and discuss them in terms of simple models.