Accurate determination of the anisotropy factors and the phase differences of Raman polarizabilities in some uniaxial crystals: the case of lithium niobate

Abstract

The present study highlights self-consistently helpful improvements dedicated to overcoming the difficulty resulting from the fitting procedure of integrated Raman intensities recorded according to the rotation crystal method described earlier. To this end, the anisotropy factors of Raman polarizabilities and the corresponding relative phases are determined within the framework of the exact mathematical derivation of the phase factors. These are the relevant parameters of the Raman efficiency relations which are numerically difficult to obtain from the fitting of the integrated areas. The present theoretical approach is then applied to the modes of the A(1) and Ey symmetry species of the lithium niobate (LN) crystal point group. All the expressions of the Raman absolute intensities of the A(1) and Ey irreducible representations initially imply three parameters to be determined from the fitting computations. However, from the derived analytical expressions of the phase differences, the number of parameters involved in the fitting procedure is reduced from 3 to 2, thus improving the statistics of the numerical treatment.

An Alternate Method for the Determination of the Raman Cross Sections of Optical Phonons in Uniaxial Crystals: Application to LiNbO<sub>3</sub>

“…The spectra were then normalised by dividing their computed areas by the area under the b (TO) mode. Are also presented in the parentheses the analogous values normalised by the area of lowest frequency A 1 modes (253 cm -1 ) as published by [13,15]. As can be observed there are not noticeable difference.…”

“…Table 1. Relative Raman Tensor elements of optical phonon for LiNbO3 normalised at the same frequencies and obtained in this work d equivalent values given by [13,15].…”

Experimental and theoretical directional dependence of optical polar phonons in the LiNbO3 single crystal: New and complete assignment of the normal mode frequencies

“…for the sake of clarity. However, the A 1 (LO) + E(TO) frequencies are measured and compared with our earlier results performed on the same sample under the backscattering scheme . We also reject the spectrum measured at the 80° angular position of the phonon wave vector due to the difficulty of obtaining redundancy of the measurements.…”