ABSTRACT
The LDV (Laser Doppler Velocimeter) is another big success of photonic instrumentation, both for scientific and industrial relevance. The LDV is once again an interferometer, but it uses two beams to illuminate a flowing fluid at the intersection of the beams, developing there a signal proportional to the speed of the fluid. After an introductory analysis of the LDV basic scheme and variants, the chapter treats the performances of the instrument - scale factor, precision, size of sensing region, placement of photodetector, direction discrimination, particle seeding, and processing of the detected signal, either time-domain or frequency-domain. A short account of new approaches to velocimetry, notably PIV (particle image velocimetry) and SMI flowmeter concludes the chapter.
