Heterodyne speckle velocimetry of Poiseuille flow

We review the technique named heterodyne speckle velocimetry and present two applications for testing the method with a fluid moving under the conditions of Poiseuille flow. The fluid was seeded with small tracking particles (diameter 300 nm) and fluxed between the two parallel planes of a cell with constant or variable cross section. In the first case the velocity distribution was constant along the direction parallel to the planes and was in excellent agreement with the expected Poiseuille profile along the orthogonal direction. In the second case, where velocity gradients were present also along the planes, the technique was able to reconstruct both the orthogonal Poiseuille profile and the in-plane two dimensional mapping of the velocity vectors, with the possibility of measuring the fluid flux within an accuracy of 1%.