The Use of High-Frequency Pulsed Laser Diodes in Fringe Type Laser Doppler Anemometry

The benefits obtained by using pulsed laser diodes with repetition rates much higher than the Doppler frequency are described and the advantages over cw- and long-pulse operation are shown. These benefits are achieved by several characteristics of pulsed laser operation. First, in pulsed mode the time-averaged number of photons may be considerably higher than in cw-mode. Second, for some of the LDA data acquisition systems the laser pulses can be synchronized with the sampling process of the acquisition systems, and third, in multiple-component systems the phases of the laser pulses in the emitter parts can be shifted with respect to each other so that one single receiver part is sufficient for all components and an identical wavelength can be used for all components. Experimental verification proves the feasibility of these conceptions.