Investigation of thermomechanical motion in a nanomechanical resonator based on optical intensity mapping

Measurement of reflected optical light from the surface of microscopic structures can offer a precise tool to investigate the oscillatory motion of micro- and nano-mechanical resonators. We demonstrate an optical investigation of multiple flexural modes of a nanomechanical resonator in thermal motion based on amplitude-modulated laser light, with higher-order resonant modes up to ~ 17 MHz measured with this technique. Scanning focused laser light reproduces the mode shape of each flexural mode, and theoretical estimation of measurement sensitivity shows a displacement sensitivity of ~ 10 ⁻¹⁵ m/Hz^1/2. For nanomechanical devices incompatible with interferometric systems, this technique can exhibit sufficient sensitivity to explore small motional states.