Non-linear speckle phase changes in the image plane caused by out of plane displacement

The speckle phase changes which occur in the image plane when the illuminated object is displaced along the optical axis are investigated. This is done by means of simulations and measurements. The object displacement is divided into a number of smaller displacement steps and by simulating the speckle phase for each step the behaviour of the phase can be visualized. It is shown how phase singularities arise and disappear during the displacement. These results obtained by numerical generation of the speckle phase are verified experimentally. The physical model used for the generation of subjective speckle fields as well as the experimental setup are described. (C) 1999 Published by Elsevier Science B.V. All rights reserved.