Fano resonance between Stokes and anti-Stokes Brillouin scattering

In recent years, the manipulation of Fano resonances in time domain has unlocked deep insights into a broad spectrum systems' coherent dynamics. Here, inelastic scattering light with acoustic phonons is harnessed to achieve complex resonances. The sudden change phonon momentum during reflection leads transition from anti-Stokes Stokes scattering, producing two different that interfere measurement process. We highlight conditions necessary such interference, revealing an underlying symmetry between photons and phonons, verify theory experimentally. Then, we demonstrate possibility characterize energy coherence losses at rough interfaces, thus providing mechanism for nondestructive testing interface quality. Our results describe numerous unexplained observations ultrafast acoustics can be generalized any waves.