1d) is as follows: a sample is installed before or behind the focal plane of Fresnel zone plate, after which a 2D diffraction pattern is recorded in the near-field zone (Fresnel diffraction).Ī schematic of CDI in the total external reflection (TER) geometry is shown in Fig. The essence of CDI in the Fresnel approximation ( Fig. 1a, but a diffraction pattern is recorded in the vicinity of Bragg reflection in the case of crystalline object (nanoscale structures, nanocrystals, etc.). The schematic of CDI in the Bragg geometry ( Fig. 1c) is similar to that presented in Fig. A ptychography experiment implies scanning over the 2D grid of extended object, with simultaneous detection of a series of diffraction patterns from partially overlapped regions of the sample studied. The latter is generally formed using a pinhole or focusing coherent optics, which includes compound refractive lenses, planar compound refractive lenses, Fresnel zone plates and a system of Kirkpatrick–Baez mirrors. In this case the linear sizes of sample studied exceed the transverse sizes of incident X-ray beam. From the experimental point of view, important features of this geometry are relatively low sensitivity to vibrations and small sample displacements and possibility of carrying out single-shot experiments under conditions of short-term (e.g., pulsed) interaction of radiation with an object studied, including the case where this interaction leads to object structure degradation (damage) or destruction.Ī schematic of X-ray ptychography is presented in Fig. A coherent X-ray plane wave is incident on a sample, which is completely illuminated, and a two-dimensional diffraction pattern is recorded in the far-field zone (Fraunhofer diffraction). To date, most of SR sources have almost 100% transverse coherence, and the upgrade of megafacilities is aimed mainly at reducing further the source emittance below 1 nm, increasing brightness, and carrying out experiments with a pico- or femtosecond temporal resolution.ĬDI in the plane-wave approximation ( Fig. Along with the development of new SR sources, a number of programs have been started that are aimed at upgrading the functioning SR sources (KSRS-Kurchatov, ESRF–EBS, PETRA IV, APS, etc.) and creating new specialized stations on the functioning sources, designed for experiments on imaging micro- and nanoobjects using CDI methods (NanoMAX on the MAX IV source in Sweden, ID16A/B and ID10 on the ESRF source in France). A particular role in the development of CDI methods belongs to Mega Science facilities: synchrotron radiation (SR) sources of the fourth generation and X-ray free-electron lasers (XFELs). The development of CDI methods makes it possible to extend significantly the range of objects studied and, correspondingly, the range of scientific problems to be solved, including such fields of prime importance in Russia as biotechnology, medicine and genetics, design of new functional (construction, composite, etc.) materials, and hybrid and nature-like technical systems (sensors, biosensors, etc.). Examples of such samples are various biological objects, including biological cells and viruses, and nanocrystallites of poorly crystallized macromolecules and their complexes. They provide amplitude- and phase-contrast imaging of an object studied and are aimed at determining the 3D structure of noncrystalline samples and nanocrystals (nanostructures) with a resolution that is theoretically restricted by only the diffraction limit. Methods based on the use of coherence of electromagnetic radiation in the X-ray range-coherent X-ray diffraction imaging (coherent diffraction imaging (CDI))-have been actively developed in the last decade.
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