Development of micro optical viscosity sensor with focus control system for in-process monitoring

We have developed a novel micro optical viscosity sensor (MOVS) based on a laser-induced capillary wave with focus control system enabling non-contact, short-time (several hundreds of nano seconds), small sample volume (several tens of micro litters), and high-stability in situ / in vivo measurement. The microfabricated MOVS chip consists of two deep trenches holding photonic crystal fibers for laser excitation, and three shallow trenches holding the lensed-fibers for probing / detecting and focus controlling. The optical interference fringe excited by two pulsed laser beams heats the sample surface, and the temporal behavior of surface geometry is detected as a first-order diffracted beam, which contains the information of liquid properties (viscosity and surface tension). In order to verify the applicability of MOVS chip for the in-process monitoring of viscosity, the preliminary measurement using acetone are demonstrated.