An Efficient Method for Determining the Output Plane of a Small-Sized Phase Object in Application to Its Image Processing

We propose an efficient method for determining the position of the output plane of a phase object, which is registered by a lens system in the presence of a defocusing effect. The method involves the simultaneous employment of 2D diffraction maps of the diffracted wave constructed for its forward and inverse directions of propagation relative to the object output plane. We show that the resultant diffraction pattern obtained for both cases of the wave propagation appears as the two opposite directed diffraction cones with a special narrow zone between them. Within such a zone, there are particular regularities in the behavior of the intensity and phase shift of the wave. The knowledge of these regularities allows one to determine the position of the object output plane with micrometer accuracy, even when a single angle of laser probing is employed.