BRILLOUIN-SCATTERING EXPERIMENT UNDER STRONG BACKGROUND LIGHT

We constructed a new system for optical beating Brillouin spectroscopy designed especially for slightly opaque samples or samples with scatt erers. The undesired effect of stray light was successfully eliminated by a new optical lock-in detection device, in which modulation of the polarization of light is employed instead of the current method of in tensity modulation, a large shot-noise component of the stray light ca n be filtered out with a lock-in amplifier. The usefulness of the syst em Nas demonstrated by a Brillouin scattering experiment in ethanol co ntaining a small obstacle, and also by an experiment of thermal phonon resonance in a microcavity.