The alteration of the frequency and the phase of light as it passes through a transparent medium. The Raman effect is caused by small differences between the energy of photons absorbed by the molecules that make up the medium and the energy of photons re-emitted.
change in the wavelength of light that occurs when a light beam is deflected by molecules. The phenomenon is named for Sir Chandrasekhara Venkata Raman, who discovered it in 1928. When a beam of light traverses a dust-free, transparent sample of a chemical compound, a small fraction of the light emerges in directions other than that of the incident (incoming) beam. Most of this scattered light is of unchanged wavelength. A small part, however, has wavelengths different from that of the incident light; its presence is a result of the Raman effect.
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