Inverse Raman effect

The inverse Raman effect in optics (the branch of physics which deals with the properties and behavior of light) is a form of Raman scattering. It was first noted by W.J.Jones and B.P. Stoicheff.

If a material is simultaneously irradiated by intense monochromatic light of frequency ν_L (typically a laser beam) and light of a continuum of higher frequencies, among the possibilities for light scattering are scattering:

• from the monochromatic beam at ν_L to the continuum at ν_L+ν_M (anti-Stokes Raman scattering)
• from the continuum at ν_L+ν_M to the monochromatic beam at ν_L (Stokes Raman scattering)

where ν_M is a Raman frequency of the material. The strength of these two scatterings depends (among other things) on the energy levels of the material, their occupancy, and the intensity of the continuum. In some circumstances Stokes scattering can exceed anti-Stokes scattering; in these cases the continuum (on leaving the material) is observed to have an absorption line (a dip in intensity) at ν_L+ν_M. This phenomenon is referred to as the inverse Raman effect; the application of the phenomenon is referred to as inverse Raman spectroscopy, and a record of the continuum is referred to as an inverse Raman spectrum.

In the original description of the inverse Raman effect, the authors discuss both absorption from a continuum of higher frequencies and absorption from a continuum of lower frequencies. They note that absorption from a continuum of lower frequencies will not be observed if the Raman frequency of the material is vibrational in origin and if the material is in thermal equilibrium.

See also

• Raman scattering
• Raman spectroscopy