Optical readout and actuation of plasmonic nano-optomechanical drum resonators

We demonstrate optical readout and actuation of nanomechanical motion using plasmonic fields in a nanoscale gap waveguide. The top gold layer of the waveguide is free to vibrate like a drumhead, and patterned with an optical grating to facilitate efficient coupling to free-space radiation. The change of the plasmonic gap mode with the top layer position couples the plasmonic resonance to the mechanical displacement of the drum. We characterize optical and mechanical resonances of the system, and demonstrate sensing of nanomechanical vibrations root with similar to 10-14 m/ Hz sensitivity. The mechanical resonators are actuated through plasmonic forces. Quantifying their magnitude shows that plasmonic forces can significantly exceed pure radiation pressure, indicating that their nature is dominated by a photothermoelastic effect. This work opens avenues to the use of plasmonic readout and control in nanomechanical sensing applications.