Figure 1: Illustration for distinguishing stimulated cavity-optomechanics from parametric cavity-optomechanics.

(a) In parametric excitation when one feeds the cavity with the laser right at the optical resonance, the pump is modulated due to a shifting optical resonance, resulting in two optical side bands accompanied by higher harmonics. If the laser is detuned, one can obtain asymmetric spectra to allow net energy transfer from light to the mechanical mode or vice versa. (b) In stimulated optomechanics (this work), the pump is scattered to only one Stokes sideband since the acoustic wave acts as a grating continuously moving away from the pump. (c) Wave vector conservation in forward Brillouin scattering leads to a much lower acoustic frequency regime when compared with backward Brillouin scattering. (d) Numerically solved optical and mechanical modes for phase-matched stimulated optomechanical interaction on a microsphere resonator, where colours represent electric field of the optical mode and the deformation of the mechanical mode. The mechanical mode (bottom-right) is a Rayleigh-type surface acoustic wave with experimentally observed frequency 57.8 MHz.