Method for optical testing of samples

Abstract

The optical testing method of the invention permits the reliable elimination of discontinuities, i.e., the determination of the integer values of modulo 2.pi. phase differences, even when the measured data includes seriously noisy signals. The intensity signals from a two-dimensional raster of camera image points are used to compute differences in phase values between adjacent image points in lines, as well as between adjacent image points in columns. The phase differences are summed along a closed path around each of a plurality of partial fields which are delineated by a predetermined set of adjacent image points. A filter (21) searches the vector field of these phase differences; and those partial fields where vortexes exist, i.e., each field for which the sign-correct sum along its closed path is not zero, are masked, thereby creating holes in the image pattern. Additional closed paths are summed around these holes and, by masking further image points between these holes, the masked partial fields are combined until the path integral around each of these combined holes disappears. The final phase value data used for display of a phase map of the sample is calculated by path integration of the unmasked image points; and inconsistent measured values, e.g., due to noisy signals, do not corrupt the phase map.