A Simple Approach to Extract Some Optical Properties of Uniaxial Crystals from the Raman Spectrum: Case of Lithium Iodate (LiIO3)
Résumé
In this work the improvement of the crystal rotation method established earlier for the quantitative analysis of the Raman spectra is presented. The integrated area is now a function of the damping parameter of the phonon modes, the phonon frequency and the maximum amplitude of the Lorentz profile. The cross sections are expressed as functions of the crystal rotation angle and the Raman polarizabilities through the anisotropy parameter. The integrated areas are fitted with a Lorentzian profile and evaluated. These areas are considered as experimental points for different crystal rotation angles to determine the angular dependence of the Raman scattering cross sections. A new nonlinear least square method (NLLSM) is used to derive the anisotropy parameters of the Raman polarizabilities and the cross sections for Transverse Optics (TO) modes. The derived quantities are later used to deduce the relative tensor of the Raman scattering cross sections. The phase differences of the Raman polarizabilities are deduced and therefore, the relative tensor of the Raman polarizabilities for the modes of the A symmetry. The angular dependence of the theoretical cross sections is also calculated for the modes of the E 1 and E 2 symmetries. The improvement of the crystal rotation method for the quantitative analysis of the Raman spectra is simple and leads to satisfactory results.