Optomechanical transduction of an integrated silicon cantilever probe using a microdisk resonator

TL;DR

This paper demonstrates a highly sensitive optical transduction method for nanoscale silicon cantilevers using a microdisk resonator, achieving high sensitivity, broad bandwidth, and dynamic range for various sensing applications.

Contribution

It introduces a monolithic cavity-optomechanical system with a nanoscale gap, enabling sensitive detection of cantilever vibrations at the microscale with high quality factors.

Findings

Achieved displacement sensitivity of ~4.4x10^-16 m/√Hz.

Bandwidth exceeds 1 GHz for vibration detection.

Observed optically-induced stiffening of the cantilever.

Abstract

Sensitive transduction of the motion of a microscale cantilever is central to many applications in mass, force, magnetic resonance, and displacement sensing. Reducing cantilever size to nanoscale dimensions can improve the bandwidth and sensitivity of techniques like atomic force microscopy, but current optical transduction methods suffer when the cantilever is small compared to the achievable spot size. Here, we demonstrate sensitive optical transduction in a monolithic cavity-optomechanical system in which a sub-picogram silicon cantilever with a sharp probe tip is separated from a microdisk optical resonator by a nanoscale gap. High quality factor (Q ~ 10^5) microdisk optical modes transduce the cantilever's MHz frequency thermally-driven vibrations with a displacement sensitivity of ~ 4.4x10^-16 m\sqrt[2]{Hz} and bandwidth > 1 GHz, and a dynamic range > 10^6 is estimated for a 1 s measurement. Optically-induced stiffening due to the strong optomechanical interaction is observed, and engineering of probe dynamics through cantilever design and electrostatic actuation is illustrated.