Optical force measurement method by a nanomechanical resonant device with electrostatic force coupling

In this study, a highly sensitive method for measuring optical forces using a nanomechanical resonant device is proposed. This device features a nanomechanical resonator electrostatically coupled to a cantilever using an applied voltage. When an optical force bends the cantilever, the electrostatic force between the cantilever and the resonator changes, enabling the measurement of the optical force by observing the corresponding shift in the resonator's resonance frequency. By structurally separating the cantilever that receives the optical force from the resonator whose vibration is measured, this device effectively reduces the influence of photothermal effects and enables highly sensitive optical force measurement even with a continuous laser. A laser was used to apply an optical force to the cantilever, and the resulting change in the resonator's resonance frequency due to the optical force was measured under various electrostatic force conditions. The experimental results achieved a best calculated optical force measurement resolution of 0.15 fN, even at room temperature and atmospheric pressure. This study suggests the existence of an optimal electrostatic force for optical force measurement, indicating the potential to achieve even higher sensitivity with the same device. Furthermore, this device-based method is expected to become a key technique for the direct measurement of optical forces. • Resonant nanodevice with reduced photothermal effects for optical force measurement. • Light irradiation and detecting parts are separated to reduce photothermal effects. • Electrostatic coupling transfers optical force effect between separated structures. • Optical force resolution of 0.15 fN at room temperature and atmospheric pressure. • An optimal electrostatic force exists to achieve the best measurement resolution.