Photon Correlation Velocimetry

Abstract

Since the first use of laser scattering to measure flow velocity by Cummins and Yen¹ in 1964 the subject has expanded continuously. The basic principle is very simple, one uses small particles, either naturally or artificially introduced into the flow, as light-scattering centres. If these particles have suitable characteristics which we shall discuss shortly, they will follow the flow faithfully and without interference and hence the light scattered in a given direction will have a time-dependent phase change related to the changing position of the particle. Using the geometry of Fig 5 of my introductory lecture the position of the scatterer is now $\mathop r\limits_ \sim \left( t \right)$ and thus the scattered field behaves as

$${E^ + }\left( {\mathop K\limits_ \sim ,t} \right)\sim {e^{i\mathop K\limits_\sim \bullet \mathop r\limits_\sim \left( t \right)}} = {e^{i\mathop K\limits_\sim \bullet \left( {\mathop r\limits_{\sim \circ } + \int\limits_ \circ ^t {\mathop v\limits_\sim \left( t \right)dt} } \right)}}$$

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