  Despite the several novel features arising from the dissipative
optomechanical coupling, such effect remains vastly unexplored due to the lack
of a simple formalism that captures non-Hermiticity in optomechanical systems.
In this Letter, we show that quasinormal-mode-based perturbation theory is
capable of correctly predicting both dispersive and dissipative optomechanical
couplings. We validate our model through simulations and also by comparison
with experimental results reported in the literature. Finally, we apply this
formalism to plasmonic systems, used for molecular optomechanics, where strong
dissipative coupling signatures in the amplification of vibrational modes are
observed.
