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Cascaded coherent Stokes Raman scattering in LiNbO 3 :Mg crystals under excitation of small polarons and phonon polaritons
Author(s) -
Kitaeva G. Kh.,
Kuznetsov K. A.,
Penin A. N.,
Solosin S. V.
Publication year - 2002
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/jrs.947
Subject(s) - polaron , polariton , raman scattering , raman spectroscopy , anharmonicity , phonon , condensed matter physics , dielectric , excitation , scattering , chemistry , molecular physics , materials science , optics , physics , optoelectronics , quantum mechanics , electron
Dispersion of the real ε′(ν) and the imaginary ε″(ν) parts of the dielectric function was measured by means of cascaded coherent Stokes Raman scattering (CSRS), in the spectral region of phonon polaritons 520–560 cm −1 , for single crystals of LiNbO 3 :Mg, before and after chemical reduction of the samples. Comparison with the results obtained by spontaneous near‐forward Raman scattering showed that the excitation of polaritons under CSRS does not cause any changes in the dielectric function of the unreduced crystal. After the reduction, which leads to the formation of localized charge carriers, small polarons, we found a sufficient increase in the dielectric function imaginary part, measured by CSRS. This reduction‐induced increase reaches its maximum values in the region of Fermi resonance between polariton and biphonon states. The possible origin of this effect, connected with the enhancement of the lattice intermolecular anharmonicity under polaron hopping, is discussed. Copyright © 2002 John Wiley & Sons, Ltd.