Speaker
Description
X-ray mirrors are essential for transporting and focusing X-rays in synchrotron radiation beamlines, thanks to their high reflectivity and minimal chromatic aberration. Recent progress in ultra-precise surface finishing and testing techniques [1-3] has enabled the creation of mirrors with accuracies reaching the 1-nm level. This has made it possible to achieve focusing down to 50-30 nm using Kirkpatrick–Baez (KB) geometry. However, sub-10 nm focusing at X-ray free-electron laser (XFEL) sources remains a significant challenge due to comatic aberration in KB geometry and unavoidable source pointing/angular jitter, which degrade the focusing conditions. Past methods used a secondary source slit to precisely define the source position, but this resulted in substantial photon loss, undermining the high-peak-brilliance characteristics of XFELs.
In this study, advanced KB (AKB) mirrors were utilized to achieve sub-10 nm XFEL beam focusing. These AKB mirrors, consisting of one-dimensional Wolter mirrors, reduce comatic aberration by satisfying Abbe’s sine condition, ensuring stable nanofocusing with greater tolerance to incident angle errors. Building on mirror characteristics and tuning strategies from previous developments in full-field imaging [4,5], we designed multilayer-coated advanced KB nanofocusing mirrors based on Wolter-type III geometry. The mirrors have been fabricated by a wavefront correction method [6,7] and achieved an accuracy of less than λ/15 in root-mean-square. Consequently, the ultra-intense XFEL sub-10 nm focusing system without the secondary source slits has been established at SACLA. The achieved focus, evaluated by the ptychography, indicated the spot size of 7 × 7 nm2 which corresponds to an XFEL intensity of 1.45 × 1022 W/cm2, representing the highest XFEL intensity ever recorded [8].
The presentation will showcase the AKB mirror development results, specifically the design and fabrication of sub-10 nm XFEL focusing mirrors, along with demonstrations of their reliable focusing performance.
References:
[1] K. Yamauchi et al., ”Figuring with subnanometer level accuracy by numerically controlled elastic emission machining”, Rev. Sci. Instrum., 73 4028–4033 (2003).
[2] K. Yamauchi et al., ”Microstitching interferometry for X-ray reflective optics”, Rev. Sci. Instrum., 74 2894–2898 (2003).
[3] H. Mimura et al., “Relative angle determinable stitching interferometry for hard x-ray reflective optics”, Rev. Sci. Instrum, 76 045102 (2005).
[4] J. Yamada et al., ”Compact full-field hard x-ray microscope based on advanced Kirkpatrick–Baez mirrors”, Optica, 7 367-370 (2020).
[5] J. Yamada et al., “Compact reflective imaging optics in hard X-ray region based on concave and convex mirrors”, Opt. Express, 27 3429-34378 (2019).
[6] S. Matsuyama et al., ”Nanofocusing of X-ray free-electron laser using wavefront-corrected multilayer focusing mirrors”, Sci. Rep., 8 17440 (2018).
[7] J. Yamada et al., ”X-Ray Single-Grating Interferometry for Wavefront Measurement and Correction of Hard X-Ray Nanofocusing Mirrors”, Sensors, 20 7356 (2020).
[8] J. Yamada et al., ”Extreme focusing of hard X-ray free-electron laser pulses enables 7 nm focus width and 1022 W cm−2 intensity”, Nat. Photon. 18 685-690 (2024).
Jumpei Yamada(1,2)
(1) Graduate School of Engineering, Osaka University, 2-1, Yamada-oka, Suita, Osaka, 565-0871, Japan.
(2) RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo, Hyogo, 679-5148, Japan.
yamada@prec.eng.osaka-u.ac.jp
