Fiber optic distributed velocity sensor for precision measurements in microscopic and macroscopic flows

We report about a laser Doppler velocity profile sensor for precision measurements of microfluidic flows. The sensor measures the velocity and position of a tracer particle in the measurement volume, which consists of two superposed interference fringe systems of different wavelength, one with convergent, one with divergent interference fringes. This arrangement was achieved with a special combination of a diffractive and achromatic lenses. Due to fiber-optic beam delivery the sensor can be build compact and offers potential for miniaturization. A spatial resolution in the sub-micrometer range and an uncertainty of the velocity of about 10 -4 could be achieved. The sensor offers potential for a variety of applications, like the investigation of shear flows or precise flow rate measurments.