Brillouin Light Scattering Spectroscopy and Its Applications

Brillouin Light Scattering (BLS) spectroscopy has emerged as a cornerstone technique for investigating elementary excitations in condensed matter systems, offering unique capabilities for non invasive characterization of magnon and phonon dynamics. This review examines the fundamental principles, technological evolution, and diverse applications of BLS across multiple research domains.<br>BLS operates through inelastic scattering between photons and quasiparticles (magnons, phonons), enabling precise measurement of excitation frequencies, propagation characteristics, and interaction mechanisms via detection of characteristic frequency shifts. Since Brillouin’s 1914 theoretical prediction and Gross’s 1930 experimental verification, the technique has evolved dramatically. The revolutionary development of tandem Fabry-Pérot interferometers by Sandercock in the 1970s established the foundation for modern high-resolution BLS systems, achieving contrast ratios exceeding 1010 and frequency resolution in the MHz range.<br>We detail four advanced BLS configurations: 1) Conventional wave-vector-resolved systems enabling precise dispersion relation measurements and detection of non-reciprocal spin wave propagation induced by Dzyaloshinskii-Moriya interactions; 2) Micro-focused BLS (μBLS) achieving sub-micrometer spatial resolution for nanoscale magnetic structure characterization; 3) Time-resolved BLS (TR-BLS) providing nanosecond temporal resolution for studying ultrafast dynamics, magnon Bose-Einstein condensation, and nonlinear phenomena; 4) Phase-resolved BLS (PR-BLS) enabling direct wave vector and phase measurements through electro-optical modulation.<br>Beyond traditional magnonic applications, BLS demonstrates remarkable versatility in phonon research and magnetoacoustic coupling studies. The technique’s polarization-sensitive detection allows simultaneous investigation of magnon-phonon hybrid states and energy transfer mechanisms. Importantly, BLS has successfully expanded into biomedical applications, providing non-contact characterization of cellular and tissue viscoelastic properties at GHz frequencies, revealing disease-related biomechanical changes.<br>As BLS technology continues advancing through improved instrumentation and novel methodologies, it serves as an indispensable platform spanning quantum materials research, magnonic device development, and cellular mechanobiology, positioning itself at the forefront of interdisciplinary science bridging condensed matter physics, materials engineering, and biomedical research.