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Optical phonons that are Raman active can also interact indirectly with light, through Raman scattering. Optical phonons are often abbreviated as LO and TO phonons, for the longitudinal and transverse modes respectively; the splitting between LO and TO frequencies is often described accurately by the Lyddane–Sachs–Teller relation.
Phonons are the main source of heat conductivity in materials, where optical phonons contribute far less than acoustic phonons. This is because of the relatively low group velocity of optical phonons. When the thickness of the material decreases, the conductivity of via acoustic also decreases, since surface scattering increases. [12]
The Raman effect is named after Indian scientist C. V. Raman, who discovered it in 1928 with assistance from his student K. S. Krishnan. Raman was awarded the 1930 Nobel Prize in Physics for his discovery of Raman scattering. The effect had been predicted theoretically by Adolf Smekal in 1923.
Optical phonons and molecular vibrations measured in Raman spectroscopy typically have wavenumbers between 10 and 4000 cm −1, while phonons involved in Brillouin scattering are on the order of 0.1–6 cm −1. This roughly two order of magnitude difference becomes obvious when attempting to perform Raman spectroscopy vs. Brillouin ...
Raman spectroscopy offers several advantages for microscopic analysis. Since it is a light scattering technique, specimens do not need to be fixed or sectioned. Raman spectra can be collected from a very small volume (< 1 μm in diameter, < 10 μm in depth); these spectra allow the identification of species present in that volume. [51]
Raman optical activity spectroscopy is related to Raman spectroscopy and circular dichroism. Recent studies have shown how by using optical vortex light beams, a distinct type of Raman optical activity that is sensitive to the orbital angular momentum of the incident light is manifest. [2]
In Raman scattering, photons are scattered by the effect of vibrational and rotational transitions in the bonds between first-order neighboring atoms, while Brillouin scattering results from the scattering of photons caused by large scale, low-frequency phonons.
Influence of Optical Activity on Raman spectre; Experimental observation of Polaritons in Ionic Crystals; Study of Oblique Phonons in Birefringent Crystals; Light Scattering by Spin Waves (Magnons) Raman Scattering by F-Centers; Enhancement of Raman Cross-sections due to Resonant Absorption; Observation of Anti-symmetric Electronic Raman Scattering
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