Velocity Measurements Using a Semiconductor Laser Doppler Anemometer

The possibilities of use of laser diodes (LD) and avalanche photodiodes (APD) were experimentally investigated with the object of miniaturizing laser Doppler anemometers (LDA) for the velocity measurement in gases and fluids.At the transmitting end laser diodes can be used in the place of the conventional gas lasers and at the detecting end photodiodes can be substituted for photomultipliers. Both index-guided and gain-guided laser diodes can be used as light sources for laser Doppler anemometers. The experimental comparison between the attainable signal-to-noise ratios of photomultipliers and photodiodes shows that particularly in the infrared region around 800 nm semiconductor diodes provide much better LDA signals than photomultipliers. The problem of wavelength stabilization of laser diodes for LDA use is discussed and a wavelength-stabilized, miniaturized laser diode LDA for backscatter applications in the velocity range up to 150 m/s is presented.