VISUALIZATION AND ANALYSIS OF A FLOW-RATE DISTRIBUTION IN A LIQUID-LIQUID TWO-PHASE FLUID USING SURFACE PLASMON POLARITONS

摘要

Optical energy propagates along the metal surface as collective oscillations of free electrons when optical waves are irradiated with the resonant condition. The oscillations with electrical fields are called surface plasmon polaritons (SPPs). SPPs are applied to sensors since excitation condition of SPPs sensitively responses to refractive indices. Here, using SPPs, a flow of a liquid-liquid two-phase fluid is visualized, and a flow-rate distribution is derived. A channel is made on the silver-film surface deposited on a slide glass, and filled with ethanol-aqueous solution. In this condition, SPPs are excited on the silver surface by Helium-Neon laser. The laser is expanded and collimated to obtain two dimensional images. Then, water is injected into the channel at a constant pressure. SPPs disappear gradually as the water comes close to near-field of the silver surface, because SPP excitation is optimized to the ethanol-aqueous solution, not to water. The SPP disappearing is visually observed in reflected light. Changes in brightness at the centre of the channel in a recorded movie are converted to changes in distance between the water layer and silver surface, based on simulation of SPP excitation. As a result, we confirmed that the flow speed of the vicinity of the silver surface is slower than that of the distant position. This flow rate distribution corresponds to a theory that a velocity gradient is caused by the shearing force between fluid and wall surface. Presented method doesn't require any tracer particles or coloring though sample fluids are clear and colorless.