Abstract
Transverse coherence of the x-ray beam from a bending magnet source was studied along multiple directions using a 2-D π/2 phase grating by measuring interferogram visibilities at different distances behind the grating. These measurements suggest that the preferred measuring orientation of a 2-D checkerboard grating is along the diagonal directions of the square blocks, where the interferograms have higher visibility and are not sensitive to the deviation of the duty cycle of the grating period. These observations are verified by thorough wavefront propagation simulations. The accuracy of the measured coherence values was also validated by the simulation and analytical results obtained from the source parameters. In addition, capability of the technique in probing spatially resolved local transverse coherence is demonstrated.
Highlights
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 [1,2,3]
We modeled the measured coherence values by performing wavefront propagation simulation using the SRW package [21]
A sinusoidal oscillation of the visibility is due to the fractional Talbot effect imparted by a 2-D checkerboard phase grating that is optimized for π/2 phase shift for 18-keV x-rays
Summary
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 [1,2,3]. 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 [8]. This has been extensively used to characterize the coherence of the beam from optical light sources [9], XUV radiation [10], synchrotron sources [11, 12], and XFELs [13]. 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. The spatial range of the coherence measurement is limited for hard X-rays [16]
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