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Depolarization

المؤلف:  Peter Atkins، Julio de Paula

المصدر:  ATKINS PHYSICAL CHEMISTRY

الجزء والصفحة:  464

2025-12-06

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Depolarization

The assignment of Raman lines to particular vibrational modes is aided by noting the state of polarization of the scattered light. The depolarization ratio, ρ, of a line is the ratio of the intensities, I, of the scattered light with polarizations perpendicular and parallel to the plane of polarization of the incident radiation:

ρ=

To measure ρ, the intensity of a Raman line is measured with a polarizing filter (a ‘half-wave plate’) first parallel and then perpendicular to the polarization of the incident beam. If the emergent light is not polarized, then both intensities are the same and ρ is close to 1; if the light retains its initial polarization, then I⊥ = 0, so ρ = 0 (Fig. 13.44). A line is classified as depolarized if it has ρ close to or greater than 0.75 and as polarized if ρ < 0.75. Only totally symmetrical vibrations give rise to polarized lines in which the incident polarization is largely preserved. Vibrations that are not totally symmetrical give rise to depolarized lines because the incident radiation can give rise to radiation in the perpendicular direction too.

Fig. 13.44 The definition of the planes used for the specification of the depolarization ratio, ρ, in Raman scattering.