Multiphysics optomechanical sensing of a liquid on the micron scale

Abstract: We present an optomechanical device platform for characterization of optical, thermal, and rheological properties of fluids on the micron scale. A suspended silicon microdisk resonator with a vibrating mass of 100 fg and an effective measurement volume of less than a pL is used to monitor properties of different fluids at rest. By employing analytical models for thermo-optical effects, thermal diffusion and fluid-structure interactions, our platform determines the refractive index, thermal conductivity, viscosity, density and compressibility of the fluid, in a compact measurement setup. A single measurement takes as short as 70 microseconds, and the employed power can be less than 100 microwatts, guaranteeing measurement at rest and in thermal equilibrium.