Angle dependence of Brillouin scattering intensity in liquids

We developed an off-axis Brillouin spectroscopy system with wide-angle tuning and polarization selection capabilities to study the angle-dependent intensity of Brillouin scattering. To compensate for variations in collection efficiency across different scattering angles, we standardized Brillouin signal intensities using Rayleigh scattering as a reference. Using a virtual imaged phased array (VIPA) spectrometer, we achieved fast, simultaneous, high-precision measurements of Rayleigh and Brillouin signals, reducing acquisition time to sub-second levels. We measured the Landau-Placzek ratio of water to be 0.015, an improvement in accuracy compared to previous reports and closer to the theoretical value of 0.01. Our results confirm that Brillouin and Rayleigh scattering share the same angle dependence, demonstrating that the dipole scattering model is well-suited for Brillouin scattering in liquids. This work establishes a simple yet robust framework for accurate spectral analysis and strengthens the applicability of Brillouin microscopy in biomechanical research.