Optomechanical intermodulation noise*

We experimentally investigate the thermal noise properties of a room-temperature, membrane-in-the-middle optomechanical cavity in the regime of nominal quantum cooperativity approaching one. We show that with resonant laser drive, the intra-cavity amplitude noise is dominated by thermal noise up-converted by nonlinear cavity transduction of the laser-cavity detuning. This noise conversion process sets a limitation on the observability of quantum features of the optomechanical interaction, which is not specific to membrane in the middle setups.