Calculations of third-order electronic susceptibility of alkali halides

Hyper-Raman scattering by the zone-center optical phonons in some alkali halides is investigated. In our calculations we relate the electrooptic part of the hyper-Raman tensor to the third-order optical susceptibility and the electric field associated with the LO phonons. The result obtained for those alkali halides for which the third-order optical susceptibility has not been measured yet, show that the electrooptic and lattice contributions to the hyper-Raman scattering are comparable. In all crystals considered, we found the cubic anisotropy of the electrooptic part of the hyper-Raman tensor to be not strongly exhibited.