Quasielastic and Low-Frequency Raman Light Scattering in Lithium Niobate Crystals with Stoichiometric Defects

The paper investigates quasielastic light scattering spectra at a temperature of 296 K in lithium niobate samples of various degrees of imperfection as measured by means of the acoustic quality factor. We performed a quantitative spectrum analysis in the 0--70 cm^-1 frequency range for samples with different Q-factor values in a model accounting for the connection between a low-frequency optical mode of the A1(TO) symmetry type and the acoustic density of states observed in a spectrum as a result of violating the wavevector selection rule in a stoichiometrically defective crystal. The results of comparing these simulations to experimental data show that stoichiometrical defects significantly contribute to the quasielastic light scattering intensity in congruent lithium niobate crystals

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