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9 September 2019 Precision focusing mirror alignment at SACLA using new nanobeam diagnosis (Conference Presentation)
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Abstract
Focusing X-ray free-electron lasers (XFELs) is very important for producing ultra-intense X-ray nanoprobes. We have developed a system based on multilayer Kirkpatrick–Baez (KB) mirrors to focus XFELs to 10 nm or less at the SPring-8 Angstrom Compact free-electron LAser (SACLA) facility. The mirror optics in the system are designed with a large NA of greater than 0.01 to produce a diffraction-limited size of 6 nm at 9 keV. We constructed a precise X-ray grating interferometer based on the Talbot effect, and succeeded in fabricating near-perfect focusing mirrors with wavefront aberrations of λ/4. However, strict error tolerances for mirror alignment can prevent sub-10 nm focusing. Errors of perpendicularity, incident angle, and astigmatism cause aberration on the focusing wavefront and characteristically change the beam shape. In particular, the required accuracy of the incident angle is 500 nrad. Due to shot-by-shot variations in the XFEL beam position and vibration of the optics, a single-shot diagnosis of beam shape is essential to align the mirrors quickly and accurately. By improving the method proposed by Sikorski et al. at the Stanford Linear Accelerator Center (SLAC), National Accelerator Laboratory, we propose a nanobeam diagnosis method based on the speckle pattern observed under coherent scattering. Computer simulation revealed that speckle size and beam size are inversely proportional. Platinum particles with a diameter of 2 nm were prepared and irradiated with X-rays to obtain a speckle pattern. Our experimental results demonstrate the successful estimation of beam shape and the alignment of all mirrors with the required accuracies.
Conference Presentation
© (2019) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Takato Inoue, Satoshi Matsuyama, Nami Nakamura, Hirokatsu Yumoto, Yuichi Inubushi, Takahisa Koyama, Taito Osaka, Ichiro Inoue, Kensuke Tono, Haruhiko Ohashi, Makina Yabashi, Tetsuya Ishikawa, and Kazuto Yamauchi "Precision focusing mirror alignment at SACLA using new nanobeam diagnosis (Conference Presentation)", Proc. SPIE 11108, Advances in X-Ray/EUV Optics and Components XIV, 1110802 (9 September 2019); https://doi.org/10.1117/12.2526972
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