Optically tunable nonlinear mechanical damping in an optomechanical resonator

We theoretically propose and experimentally demonstrate optically tunable nonlinear mechanical damping in a cavity optomechanical system utilizing a partly resolved sideband regime. Optomechanical coupling provides a delayed nonlinear backaction to the mechanical modes, resulting in nonlinear mechanical damping. This optically induced nonlinear damping is observed in the frequency and time domains, and we show using both theory and experiment that it can be tuned via laser detuning. We also observe optically mediated cross-nonlinear damping between two mechanical modes: the amplitude of one mode modulates the damping of the other. The presented results show a fully tunable scheme of nonlinear mechanical damping that will be applicable to various non-trivial systems, governed by nonlinear, nonequilibrium, and non-Hermitian phenomena.

💡 Research Summary

The paper presents a combined theoretical and experimental study of optically tunable nonlinear mechanical damping in a cavity optomechanical system operating in a partially resolved sideband regime (κ_cav ≈ Ω_m). The authors show that when the cavity decay rate becomes comparable to the mechanical resonance frequency, the radiation‑pressure back‑action acquires a finite delay. This delayed back‑action generates a non‑conservative component in the mechanical force, which manifests as a cubic (amplitude‑dependent) damping term.

Starting from the coupled equations for the optical field amplitude a(t) and mechanical mode amplitudes b_j(t), the authors solve the optical equation formally and substitute the result back into the mechanical equation, obtaining a memory‑kernel description that yields third‑order nonlinear terms. For a single mechanical mode the effective equation of motion reads

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