Raman scattering by longitudinal and transverse optical vibrations in lithium niobate single crystals

Raman spectra of single-domain congruent lithium niobate crystals have been measured in forward-axis and backscattering geometries, with excitation laser light propagating along or across the ferroelectric axis Z. We have identified excitation conditions for transverse and longitudinal A1(Z) polar optical modes in room-temperature Raman spectra. The general aspects of the excitation of Raman spectra have been studied in several polarization geometries: Z(XX; YY; XY)Z, Z(XX; YY; XY)\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\bar Z$\end{document}; X(ZZ)X; Y(ZZ)Y, and X(ZZ)Y. The excitation conditions for coherent longitudinal and transverse modes in lithium niobate single crystals in the case of stimulated Raman scattering have been analyzed.