Spatially-resolved velocity profile measurements by means of a two-wavelength technique

A measuring system based on a differential laser-Doppler anemometer has been extended to determine one-dimensional velocity profiles of shear flows with a spatial resolution in the micrometer range. The principle of the realised velocity profile sensor is based on two-wavelength fringe systems with different gradients of their fringe spacings. After wavelength-sensitive detection two Doppler frequencies are determined, which yield the position as well as the velocity component of individual tracer particles.