Evanescent wave Doppler velocimetry for a wall's near field

This study proposes a Doppler velocimetry utilizing evanescent waves that are induced by a laser beam. This velocimetry allows us to measure the flow velocity within the near field less than 1 μm from a dielectric surface. When evanescent waves propagate in opposite directions on a dielectric surface, the waves interfere with each other and produce a standing wave within the near field. When a tracer particle goes through the standing wave, the particle scatters the wave. The flow velocity within the near field can be determined by measuring the blinking frequency similar to conventional laser Doppler velocimetry. The validity of this velocimetry is empirically examined by applying it to a slip velocity measurement of a solid on a dielectric surface.