X-Ray Lensless Optics and Ptychography

One of the tasks of modern optical methods is the most complete description of the objects under study and the wave fields. For example, properties of the materials under study should be characterized not only by absorption but also by refraction, and the wave fields behind the object and near the detector should be characterized not only by intensity but also by phase. The work of Gerchberg and Saxton in 1972 was the first attempt to accomplish this task without using any optical elements, relying only on a quadratic detector and a computer simulation of the propagation of electromagnetic waves. Today, similar lensless imaging methods are applied across a wide range of wavelengths—from terahertz to hard X-ray. The purpose of this paper is to provide a brief introduction to the theory of lensless methods as applied to the X-ray wavelength range. It also presents the results of recent experiments on lensless imaging of test objects conducted at the Lebedev Physical Institute using lasers.