However, for hard x-rays, fabrication of high aspect ratio amplitude gratings (either 1-D or 2-D) is very challenging. This technique is model-free and requires only a very simple experimental setup and easy data processing. measured the complex coherence function (CCF) from decaying visibility of fractional Talbot distances. Using two gratings and generating a Moiré pattern, F. ĭifferent from the above-mentioned techniques, a periodic phase object can be used to generate fractional Talbot images, and the evaluation of these images as a function of defocusing distance provides information about the transverse coherence of the beam. The spatial range of the coherence measurement is also limited for hard X-rays. Though the technique can measure the full coherence of the x-ray beam with a single interferogram, it is not model-free and requires knowledge of the detailed structure of the URA as an input for the data deconvolution. for soft x-ray beams, where a uniformly redundant array (URA) was utilized as a phase-shifting mask to measure the coherence property of the undulator radiation. ![]() introduced a different technique first used by K. To obtain the full complex coherence function (CCF) of the beam requires a series of measurements with variable slit separations and positions, which is time consuming and therefore not practical. This has been extensively used to characterize the coherence of the beam from optical light sources, XUV radiation, synchrotron sources, and XFELs. The typical and most widely used method to demonstrate the transverse coherence effect is by generating an interference pattern using the Young’s double pinhole/slit arrangement. ![]() With respect to matching the beam properties with the sample, it is essential to characterize the incident x-ray source in all transverse directions at the sample position. Therefore, it is becoming important to characterize the beam coherence as well as the degradation of coherence and changes in the wavefront due to the optical elements along the beam path. Also there are other lab-based sources, such as standard x-ray tube sources, tabletop soft x-ray sources, and compact light sources, that are being increasingly used for x-ray microscopy/imaging experiments. With the advent of brilliant and highly coherent x-ray sources like the third-generation synchrotron radiation facilities and x-ray free electron lasers (XFELs), the number of experiments using the coherence property of the source, such as coherent diffraction imaging (CDI), holography, and x-ray microscopy, has increased tremendously.
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