Cavity enhanced cw stimulated Brillouin scattering in a fused silica plate

We have observed cavity enhanced stimulated Brillouin scattering (SBS) in a high finesse optical ring resonator. Brillouin scattering occurs in a fused silica plate placed in the focus of the light beam inside the cavity. The frequency spacing of the Brillouin scattered wave relative to the incident beam at 23.5 GHz has a linewidth of less than 500 Hz. In preliminary experiments we extracted a scattered optical power of 25 mW from the resonator. Possible applications are discussed.