Measuring principle of the Laser-Doppler-Velocimetry (LDV)

At least two laser beams are brought to intersect. At this generated measuring volume an interference fringe pattern is formed. When a particle (e.g. airbubble or seed particle) crosses this light/dark pattern, it scatters and modulates the laser light. The received frequency of the scattered light is directly proportional to the velocity of the particle in the measuring point. So it is possible to measure the punctual velocity in fluids with a high resolution and multidimensial determined.