We describe a point diffraction interferometer (PDI) for use in
connection with stressed fluids. Since the wavefront distortions are
conspicuous, the transmitted field breaks down into a speckle distribution.
A speckle chaser has been devised so that a bright speckle is
always kept on top of the PDI pinhole. Adequate power for the selfgenerated
reference beam is thus available, and fringe visibility remains
quite satisfactory even for large optical distortions.