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Reference Beam Laser Doppler Anemometer (RSS-LDA)

In the illuminating beam a photodiode placed into the reference beam (for a normal LDA the receiver is always outside the beams) sees a fringe pattern that can be used to measure velocities. Compared to a standard LDA the measuring volume is not limited to the cross section of beams. The size of the measuring volume is inversely proportional to the diameter of the receiver (coherence cone).