A detailed experimental and theoretical study of the Raman spectrum of the orthorhombic piezoelectric crystal LiGa${\mathrm{O}}_2$ is presented. The 45 fundamental modes were analyzed with respect to their frequency and intensity and a classification into symmetry species and LO-TO splitting is obtained. From these results the angular dispersion and the infrared absorption spectra were calculated and found to be in very good agreement with experimental results. It is shown that from a complete set of classified modes the effective charge parameters, the Raman tensor components including their signs, the nonlinear-optical tensor, and the electro-optical tensor can be derived. In addition a relation for the nonlinear susceptibility as a function of the frequency was obtained which exhibits characteristic resonances at the fundamental phonon frequencies. Results evaluated for LiGa${\mathrm{O}}_2$ showed that the nonlinear-optical tensor for this crystal is very small.

• Received 22 February 1983

DOI:https://doi.org/10.1103/PhysRevB.29.2221