Determination of velocity gradients with scattered light cross-correlation measurements.

The space-time correlation function of the intensity of light scattered off a medium with a constant velocity gradient has been calculated. One property, in particular, of this correlation function, which may be referred to as speckle motion or speckle flow, enables an experimental determination of the tensor components of the velocity gradient. Influence of Brownian motion and finite scattering volume are estimated. Experimental results, obtained at a tube flow, are shown to be in accordance with the theory.