  Energy exchange between light and sound was first suggested by Brillouin in
1922. After Townes established the phonon maser theory, coherent generation of
intense hypersonic waves was observed together with stimulated Brillouin
Scattering. Here we repeat these experiments, but with capillary-waves that are
unique to the liquid phase of matter and relates to attraction between intimate
fluid particles. We fabricate resonators that co-host capillary and
opticalmodes, control it to operates at its non resolved sideband, and observe
stimulated capillary scattering and coherent excitation of capillary resonances
at kHz rates (that one can hear in audio files recorded by us). By exchanging
energy between electromagnetic and capillary waves, we bridge interfacial
tension phenomena at the liquid phase boundary to optics, and might impact
optofluidics by allowing optical control, interrogation and cooling of water
waves.
