A cavity-based X-ray free-electron laser (CBXFEL) is a possible future direction in the developme... more A cavity-based X-ray free-electron laser (CBXFEL) is a possible future direction in the development of fully coherent X-ray sources. CBXFELs consist of a low-emittance electron source, a magnet system with several undulators and chicanes, and an X-ray cavity. The X-ray cavity stores and circulates X-ray pulses for repeated FEL interactions with electron pulses until the FEL reaches saturation. CBXFEL cavities require low-loss wavefront-preserving optical components: near-100%-reflectivity X-ray diamond Bragg-reflecting crystals, outcoupling devices such as thin diamond membranes or X-ray gratings, and aberration-free focusing elements. In the framework of the collaborative CBXFEL research and development project of Argonne National Laboratory, SLAC National Accelerator Laboratory and SPring-8, we report here the design, manufacturing and characterization of X-ray optical components for the CBXFEL cavity, which include high-reflectivity diamond crystal mirrors, a diamond drumhead crystal with thin membranes, beryllium refractive lenses and channel-cut Si monochromators. All the designed optical components have been fully characterized at the Advanced Photon Source to demonstrate their suitability for the CBXFEL cavity application. research papers 752 Peifan Liu et al. � X-ray optics for cavity-based XFEL J. Synchrotron Rad. (2024). 31, 751-762 Figure 1 An overview of the experimental setup of the cavity-based X-ray free-electron laser (CBXFEL) project, which consists of an electron beam source, a cascade of undulators and two chicanes, and a rectangular X-ray cavity. The X-ray cavity consists of four diamond crystal mirrors (C 1-C 4), reflecting X-rays in the 400 Bragg reflection at exactly 45 � with a photon energy of 9.831 keV, and two X-ray lenses (L 1 , L 2). Diamond crystal C 1 has a drumhead crystal structure (Kolodziej et al., 2016) with a �20 mm-thick membrane to outcouple X-rays (Kim et al., 2008; Kim & Shvyd'ko, 2009; Shvyd'ko, 2019) to diagnostics station G in the X-ray pump-probe (XPP) LCLS experimental hutch, which is located �250 m downstream of the undulators (Chollet et al., 2015). In station G, Si channel-cut monochromator crystals (CC) will be used to monochromatize the broadband X-rays to a narrow band centered on 9.831 keV for further diagnostics. A thin diamond C x in the 440 exact Bragg backscattering is used for precise energy calibration and C 1 angular alignment. The long-arm length L of the rectangle is 32.10 m and the short-arm length W is 0.65 m. A diamond grating (Li et al., 2020) downstream of C 2 will also be used for alternative output coupling for X-ray diagnostics in station E. The upper-left inset (a) shows the total reflectivity of the four diamond crystals and transmissivity of the drumhead crystal C 1 , with a drumhead membrane thickness of (left) 20 mm and (right) 15 mm. research papers
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Papers by Keshab Kauchha