Virtual Lens Method for Near-Field Phase Retrieval

—The progress in the computer science caused wide acceptance of lensless imaging methods, in particular, the phase reconstruction method. It allows phase and amplitude distribution reconstruction in the object plane by mathematical treatment of the diffraction pattern resulting from a coherent beam passage or reflection from an object. In this case, elements of conventional optical systems, i.e., lenses, focusing mirrors, and others are not used. The classical version of the method implies the detector position in the far-field region with respect to the object, which simplifies calculations. However, this condition is not always feasible; therefore, near-field method versions based on the direct application of the wave propagator were proposed in some studies. In this paper, a new version based on a virtual lens is proposed. Then the complexity and computation time remain at the same level as for the far zone, but it is possible to significantly reduce the distance to the detector. The effectiveness of the method is demonstrated in an experiment with a helium-neon laser.