Laser and avalanche diodes for velocity measurement by laser Doppler anemometry

The paper describes the possibilities of using semiconductor components for laser Doppler anemometers. This includes laser diodes D at the transmitting optics and PIN and avalanche diodes at the receiver. The advantages and disadvantages of various laser diode types are described, reference is made to problems such as focussing and wavelength stabilization and practical hints are given for the use of LDA. Extensive measurements of the attainable signal-to-noise ratios (SNR) of photomultipliers and of a number of photodiodes of different make have shown that some photodiode models are now superior to photomultipliers. Laser diodes should be used together with photodiodes to construct miniaturized laser Doppler anemometers, as such semiconductor LDA are much more efficient than conventional anemometers with gas lasers and photo-multipliers. Moreover, miniaturized LDA designs can now also be used for battery operation and field application.