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 A 1(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) Z ; 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.