Practical LDA Configuration

A number of different optical configurations were proposed during the earlier days of laser-Doppler anemometer systems, they can all be classified as special interferometers in which one of the following interference effects occurs [58]  

Scattered light from one laser beam interferes with un-scattered light from another beam (reference beam anemometer). 

Light scattered from a single beam in two different directions interferes (single beam or two scattered beam anemometer). 

Laser-Doppler velocimetry requires a light signal that oscillates at the Doppler shift frequency. This is usually obtained by subtracting the illuminating wave frequency 

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