HIGH-RESOLUTION RAMAN MEASUREMENTS OF THE TEMPERATURE-DEPENDENCE OF THE PHONON LINEWIDTH IN LITHIUM FORMATE MONOHYDRATE CRYSTALS

Using a coupled interferomcter-spectrometer with a resolution < 0.01 cm-1 we have measured the Raman linewidth and integrated intensifies of some external modes (79 and 104 cm-1 A1 modes, 76, 131 and 173 cm-1 A2 modes and 82, 113 and 163 cm-1 B1 modes) and of the internal A1 mode at 1372 cm-1 of lithium formate monohydrate in the temperature range 10-300 K This material is an efficient nonlinear crystal with interesting electro-optic properties and technical applications. The spontaneous Raman data were analyzed and interpreted in terms of phonon relaxation by three-phonon down and up process, which are desribed by the cubic anharmonicity of the interaction potential. The data were also used for the explanation of the temperature dependence of the threshold intensity for stimulated Raman scattering. © 1990.