Optomechanical viscometer

Recently, the first microfluidic optomechanical device driven by radiation pressure – and capable of operating with non-solid states of matter (viscous fluids, bioanalytes) – was demonstrated. Here we show that the vibrational noise spectrum of the device mechanical modes enables quantification of the viscosity of fluids inside the device. A linear relation between the spectral linewidth and square root of viscosity is predicted and experimentally measured in the low viscosity regime. For the first time, an all-optical sensor of liquid viscosity using a microfluidic optomechanical resonator is demonstrated. Our result is a step towards performing high-frequency studies of fluids and boundary layer viscosities, and performing high-throughput viscoelastic measurements on flowing cells.