Brillouin Scattering

A Nonlinear Scattering effect involving acoustic phonons.

Brillouin Scattering is an effect caused by the χ(3) nonlinearity of a medium, specifically by that part of the nonlinearity which is related to acoustic phonons. An incident photon can be converted into a scattered photon of slightly lower energy, usually propagating in the backward direction, and a phonon. This can occur spontaneously even at low optical powers, and can become very strong as a stimulated effect which occurs above a certain Threshold Power of a Light beam in a medium. Above the threshold, Stimulated Brillouin Scattering can reflect most of the power of an incident beam. This process involves a strong nonlinear optical Gain for the back-reflected wave: an originally weak counterpropagating Wave at the suitable optical Frequency can be strongly amplified.

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