Interference Patterns of Two Focused Gaussian Beams in an LDA Measuring Volume

Based on a model of spherical Gaussian beam interference, the fringe spacing variations in the measuring volume of a differential LDA system are analysed and the fringe patterns are obtained for different locations of beam waists. It is found that when the incident beams are sharply focused and a large beam cross-angle is used to obtain high spatial resolution, fringe gradients occur along both the x- and z-directions, even though the incident beams intersect at their waists. When the measuring volume is very small, the measurement accuracy of an LDA is limited by inherent fringe gradients mainly along the z-direction. © 1997 Elsevier Science Ltd. All rights reserved.