Miniaturized Optical Viscosity Sensor based on a Laser-induced Capillary Wave

A novel micro optical viscosity sensor (MOVS), by laser-induced capillary wave method enabling us non-contact, short-time (several hundreds of nano seconds), and small sample volume (several tens of micro litters) in situ/in vivo measurement, is reported in this paper. The microfabricated MOVS chip consists of two deep trenches holding photonic crystal fibers for excitation laser, and two shallow trenches holding the lensed-fibers for probing laser. 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). The preliminary measurements using distilled water and sulfuric acid with dye of carbon black are demonstrated. The high-speed damped oscillation signals are successfully detected by MOVS.