Optical excitation and detection of 1-pm-order mechanical oscillation in sub-wavelength-scale plasmomechanical system

We present a sub-wavelength-scale plasmomechanical system consisting of an Au/hydrogen silsesquioxane (HSQ) plasmonic nano-resonator and a supporting HSQ nano-wall. The full footprint of the system in three dimensions is only ~0.15 μm^3, which is just ~0.59 times of cubic wavelength. Strong optical scattering and dissipation of plasmonic resonance enable interaction with mechanical motion. We experimentally demonstrate the optical excitation and readout of the fundamental longitudinal mechanical oscillation, of which the real displacement is in the order of pico-meter. The plasmonic resonance with a wide spectral width allows the optical measurement of the mechanical oscillation signal over a large wavelength range (>100 nm) of the probe laser. Our dissipatively coupled plasmomechanical system shows not only tunability of the resonance frequency of mechanical oscillation but also the thermoelastic damping effect on the mechanical quality factor depending on the pump laser power.