Scattering, Inelastic: Brillouin

Brillouin light scattering (BLS), in its historical sense, is the inelastic scattering of light by acoustic phonons. It thus provides information on the elastic properties of the scattering medium and it has been used to study gases, liquids, crystals, polymers, glasses, semiconductors, nontransparent thin layers, and superlattices. BLS yields information similar to that obtained using ultrasonic techniques but it has certain advantages when dealing with small samples, reactive samples, or in cases where contact with a transducer poses experimental difficulties (e.g., high temperatures and pressures). The Fabry–Perot interferometer (FP) is, par excellence, the instrument of choice to achieve the 1–100 GHz resolution required in typical BLS experiments. Because of this, BLS has become synonymous for all experiments performed with an FP independent of whether the scattering is produced by acoustic phonons, by magnons, or by electronic states. Here BLS is used in this broader context. This article provides a brief historical review and a condensed description of the origin of the effect. Also, some key experimental aspects are briefly described. The emphasis of this article is to illustrate, via specific examples, the range of problems that can be investigated using BLS. This will include the determination of elastic constants with emphasis on its application under adverse experimental conditions (temperature, size, and pressure), as well as its application to magnetic systems and electronic levels.