On the Far Infra Red Excitation of LO Vibrations in Thick Single Crystals |
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Authors: | Armand Hadni Xavier Gerbaux |
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Affiliation: | 1. Laboratoire Infrarouge Lointain, Université Henri Poincaré, Nancy 1 B.P. 239, F-54506, Vand?uvre-lés-Nancy Cedex, France
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Abstract: | New experiments show that the solution of the complicated problem of Far Infrared (FIR) absorption by crystals of very low symmetry, illuminated at quasi-normal incidence, might have a simple solution, which has been suggested now that a number of spectroscopic studies on monoclinic Triglycine Sulphate (TGS) are available: i) in a first classical approximation where only the strongest bands are considered, the absorption spectrum depends only on the direction of the electric field E of the IR radiation, and Transverse Optic (TO) vibrations are directly excited with electric dipole variations dp parallel to E. ii) in a second approximation looking only at the weakest absorption bands, it depends only on the direction of the wave vector k and Longitudinal Optic (LO) vibrations are excited with dp parallel to k and extinction coefficients 3 orders of magnitude smaller. |
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