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.
In this work we report on numerical investigations of the effect of the light beam divergence or imperfect crystal alignment on the response of electrooptic modulators. Resulting non linearities are discussed both in terms of nonlinear distortion of modulators and as related to errors in measurements of quadratic electrooptic coefficients. Our calculations based on the Jones calculus have been performed for uniaxial crystals including KDP, and its isomorphs, and LiNbO<SUB>3</SUB>. The results obtained confirm that either the response of the modulators or results of electrooptic measurements can be significantly affected by the light divergence or imperfections in the crystals alignment.
Applications of the bond polarizability model to various nonlinear phenomena in crystals are shown. Special attention is paid to second harmonic generation, nonlinear refractive index and hyper-Raman scattering.
Previous measurements of quadratic electrooptic coefficients in the KDP family of crystals have been analyzed. In addition, the quadratic electrooptic coefficient n<SUB>o</SUB><SUP>3</SUP>g<SUB>1111</SUB>-n<SUB>e</SUB><SUP>3</SUP>g<SUB>3311</SUB> of KDP and ADP has been measured by means of the dynamic polarimetric method. The results obtained confirm that quadratic electrooptic coefficients of KDP-type crystals are of the order of magnitude of 10<SUP>-20</SUP> m<SUP>2</SUP>V<SUP>2</SUP>. This is about 100 times smaller than values widely cited in the literature obtained by other authors employing the static polarimetric technique.