Optomechanical Transduction of an Integrated Silicon Cantilever Probe Using a Microdisk Resonator

Sensitive transduction of the motion of a micro-scale 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 subpicogram silicon cantilever with a sharp probe tip is separated from a micro disk optical resonator by a nanoscale gap. High quality factor (Q approximate to 10(5)) microdisk optical modes transduce the cantilever's megahertz frequency, thermally driven vibrations with a displacement sensitivity of approximate to 4.4 x 10(-16) m/(Hz)(1/2) 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.