ABSTRACT
Brillouin light scattering (BLS) is a noncontact measurement technique that exploits light scattering to probe the properties of ultrasonic waves, either bulk waves propagating in transparent solids or liquids or surface acoustic waves (SAWs) propagating at the surface of homogeneous solids or of thin layers, either supported or freestanding. While most other techniques require the excitation of ultrasonic waves and/or their propagation over macroscopic distances, the peculiarity of Brillouin scattering techniques is that they rely on spontaneous thermal ¢uctuations in the acoustic modes and on their detection by local inelastic scattering of light, a contactless and massless probe. This is akin to Raman scattering but entailing acoustic modes rather than molecular vibrations (in microscopic terms, long wavelength acoustic phonons rather than optical phonons).
