X-ray beam-shaping refractive optics and its applications
The most advanced X-ray sources, such as third-generation synchrotrons and free electron lasers (XFEL), are capable to generate high brightness coherent radiation, especially in the hard X-ray region. The availability of such beams facilitates to the development of a new generation of X-ray optics, which goes far beyond simple focusing optical elements. This optics possesses new optical functions, which allow forming the intensity of the wave front with almost complete freedom. Such beam-shaping elements use the most outstanding properties of synchrotron radiation such as brightness, monochromaticity and coherence. As for the possible employment of X-ray beam-shaping devices based on refractive optics, is not limited to beam conditioning applications only. It can be extended to the field of interferometry, coherent diffraction, phase-contrast microscopy, ultrafast and nonlinear optics studies.
For example, one of the most striking demonstrations of the beam-shaping optics is a special class of refractive optical elements having axial symmetry that are capable to convert a point-like source to a narrow axial straight line segment. These optical elements are called axicones. Recently, we demonstrated an X-ray parabolic refractive axicon lens as a novel type of X-ray beam-shaping element . Under coherent X-ray illumination, the parabolic axicon generates Bessel-like beam propagated along the optical axis and ring-shaped beam in the far field. Such optical transformations can be used in areas requiring special illumination, as well as extended focused beams, for instance, in diffraction and imaging techniques, in metrological, source diagnosis and beamline alignment applications. Moreover, such beam-shaping capabilities can significantly simplify some existing experimental layouts or lead to completely new optical schemes for X-ray techniques based on synchrotron and XFEL sources.
The work was supported by the Ministry of Education and Science of the Russian Federation grant contract № 14.Y26.31.0002.
 D. Zverev, A. Barannikov, I. Snigireva and A. Snigirev, Optics Express 25 (2017) 28469–28477.