Methods of synchrotron radiation monochromatization (research review)

The paper presents an analysis of studies related to the monochromatization of X-ray radiation (XR) at synchrotron radiation sources. A review of monochromators based on of X-ray diffraction on crystals is given, and the peculiarities of their technical realization are considered. The ideas about monochromators which include multilayer structures are examined. The authors also study technical problems arising during designing devices and its possible solutions. Introduction. The possibilities of using X-rays in scientific research are described. The high efficiency of synchrotron radiation sources is noted, and its characterization is given. Elementary information about diffraction of X-rays. The paper describes the properties of X-ray radiation and the possibilities of its using while studying various materials. Degree of monochromaticity. The degree of monochromaticity is an important characteristic of the synchrotron radiation (SR). Depending on the width of the wavelength band, “white”, “pink” and monochromatic beams are distinguished. Monochromators based on multilayer structures are used to obtain “pink” beams. Monochromatic radiation is formed using monocrystals. When conducting experiments with “white” beams, the monochromator is not used. The authors also describe the factors that violate the ideal fulfillment of the Wolf-Bragg condition and affect the degree of monochromaticity (heat, vibration). The reflectivity values at different beam grazing angles are noted to have different widths. Monochromators based on multilayer structures. Periodic structures combining thin layers of two heterogeneous materials make it possible to obtain “pink” beams. The wavelength bandwidth of such devices is one or two orders of magnitude greater than that of monochromators using crystals as optical elements. Configurations and geometry of optical elements. There are two types of X-ray diffraction on a crystal: Bragg and Laue diffraction. Bragg diffraction refers to reflective geometry, Laue diffraction is based on the passage of beams through the crystal. The section provides examples of monochromators with different configurations of crystals and X-ray mirrors. The arrangement of optical elements in a monochromator plays an important role in the geometry of the beam path. When designing monochromators, it is necessary to take into account the methods of fixation and orientation of the rotation axes of optical elements. Examples of monochromators with different configurations of crystals and X-ray mirrors are given. Focusing monochromators. It is possible to provide sagittal and meridional types of deformation by bending the optical element of the monochromator. Due to the curved crystal surface the beam is not only monochromatized but also subjected to focusing. Modern focusing monochromators are equipped with adaptivity elements allowing it to change the radius of curvature of the optical element. Examples of practical realization of such monochromators are presented. Thermal load of SR on optical elements. The SR is characterized by high brightness and a wide spectrum of emitted wavelengths. While operating optical elements of SR stations absorb a large amount of thermal power. The problems of heat dissipation have a fundamental influence on the quality of synchrotron radiation monochromatization. Additional information about monochromators. Examples of special design solutions for monochromators are given. Conclusion. The design of monochromators is relevant to the synchrotron radiation source 4+ “SKIF” under construction in Novosibirsk.