Coherence, as a core element of cutting-edge X-ray research technology, has driven the vigorous development of many experiments such as coherent X-ray diffraction imaging and X-ray holography in the past two decades, and has also promoted the construction of fourth generation synchrotron radiation sources and hard X-ray free electron lasers. To measure the size of synchrotron radiation light source and coherence of beamline, an X-ray measurement system based on 2D single grating interferometry was established. Conduct research on the measurement principles and propagation models used in the system. Firstly, based on the VanCittert-Zernike theorem, the relationship between the visibility of the interference lattice and the spatial coherence of X-rays is given. Secondly, combined with the Talbot self imaging effect of a single grating, the X-ray spatial coherence length of the plane where the grating is located is measured, and the spatial distribution of the corresponding light source is obtained through further calculation. The relevant measurement experiments of this study were conducted at the BL09B bending magnet beamline of the Shanghai Synchrotron Radiation Facility (SSRF). A 2D checkerboard π phase-shift grating was used as the core device in the experiment. This setup not only enabled the acquisition of transverse coherence lengths in the vertical and horizontal directions but also further measured the transverse coherence lengths in the directions forming 45° and 135° angles with the horizontal direction. The experimental process strictly followed the technical specifications outlined in this paper: along the beam propagation direction, interferograms were measured at different positions downstream of the phase grating. For each interferogram, the corresponding visibility values were extracted by analyzing the harmonic peaks in its Fourier-transformed image. Ultimately, the transverse coherence length in each direction could be derived based on the evolution law of visibility as a function of the grating-to-detector distance. The experimental results show that the coherence length of the emitted X-rays on SSRF testline is 4.2 μm (H)ｘ13.8 μm (V) @ 15 keV, and the size of the bending magnet source is 124 μm (H)ｘ38 μm (V). The results obtained by this method can provide important references for measuring the electron source size and the development of experimental methods with high requirements for uniform illumination.
Xue et al. (Wed,) studied this question.