Brillouin scattering

The Brillouin scattering is a type of optical scattering on an interaction of optical waves with acoustic lattice vibrations ( acoustic phonons) or magnetic spin-wave ( magnon ) is based. Leon Brillouin predicted this type of scattering for the first time theoretically. 1930, this prediction was confirmed experimentally.

Phonon scattering

When a photon interacts with a solid or a liquid, it can come to the energy transfer to acoustic or optical phonons. The inelastic scattering of photons by acoustic phonons is called Brillouin scattering. The inelastic scattering of the optical phonon is called Raman scattering.

Maximum scattering in the reverse direction occurs when the reflected light components overlap in phases, which occurs only with exact adjustment of light and sound wave. Brillouin scattering is therefore has an extremely frequency selective effect of 20 to 100 MHz ( frequency of the sound ). The reflected light results in a reduction of the frequency of about 1-15 GHz ( about 1-10 ppm change ) due to the Doppler shift.

Plays a role in the effect of optical amplifiers which are able to amplify optical signals without converting the optical signal to advance to an electrical.

Stimulated Brillouin scattering ( SBS) can be used for optical phase conjugation.

Scattering on magnons

The inelastic scattering of photons at magnon has a scattering cross-section smaller than the phonon scattering, but can be observed by high resolution interferometer. Due to the spin-orbit coupling, a phase grating is generated in the refractive index of the medium, which propagates at the speed of the spinning shaft. Light is diffracted by this phase grating, wherein the frequency of the light is adjusted by the spin-wave frequency is Doppler shifted. The Doppler shift is made at the higher (lower ) frequencies, when the spinning shaft in the opposite (same ) direction as compared to the component of the incident light, which is parallel to the diffusing surface, propagates.