Energy characteristics of a signal from a laser Doppler anemometer in the case of partial spatial coherence of the probe radiation

A calculation is made of the correlation function and of the energy spectrum of the signal from a single-beam heterodyne laser Doppler anemometer under conditions of partial spatial coherence of the probe beam. This partial coherence is an unavoidable factor, for example in studies of the flow in blood-carrying capillaries and living cells. The results are reported of an experiment in which the Doppler spectra were recorded for water carrying particles of polystyrene latex in a planar glass channel 200μ thick. The coherence of the probe beam was degraded by phase screens placed in front of the channel. It was found that broadening of the spectra was governed by the transit time of particles crossing a region of the order of the correlation radius of the radiation field in the measurement zone.