Stitching interferometry for ellipsoidal x-ray mirrors

Ellipsoidal mirrors, which can efficiently produce a two-dimensional focusing beam with a single mirror, are superior x-ray focusing optics, especially when compared to elliptical-cylinder mirrors in the Kirkpatrick-Baez geometry. However, nano-focusing ellipsoidal mirrors are not commonly used for x-ray optics because achieving the accuracy required for the surface metrology of nano-focusing ellipsoidal mirrors is difficult due to their small radius of curvature along the short ellipsoidal axis. Here, we developed a surface metrology system for nano-focusing ellipsoidal mirrors using stitching interferometric techniques. The developed system simultaneously measures sub-aperture shapes with a microscopic interferometer and the tilt angles of the sub-aperture shapes with a large Fizeau interferometer. After correcting the systematic errors included in the sub-aperture shapes, the entire mirror shape is calculated by stitching the sub-aperture shapes based on the obtained relative angles between partially overlapped sub-apertures. In this study, we developed correction methods for systematic errors in sub-aperture shapes that originated from off-axis aberrations produced in the optics of the microscopic interferometer. The systematic errors on an ellipsoidal mirror were estimated by measuring a series of tilted plane substrates and the ellipsoidal substrate. From measurements of an ellipsoidal mirror with a 3.6-mm radius of curvature at the mirror center, we obtained a measurement repeatability of 0.51 nm (root-mean-square) in an assessment area of 0.5 mm × 99.18 mm. This value satisfies the requirements for surface metrology of nano-focusing x-ray mirrors. Thus, the developed metrology system should be applicable for fabricating nano-focusing ellipsoidal mirrors.Hirokatsu Yumoto, Takahisa Koyama, Satoshi Matsuyama, Kazuto Yamauchi, and Haruhiko Ohashi, "Stitching interferometry for ellipsoidal x-ray mirrors", Review of Scientific Instruments 87, 051905 (2016) https://doi.org/10.1063/1.4950714

Towards high-resolution ptychographic x-ray diffraction microscopy

Ptychographic x-ray diffraction microscopy is a lensless imaging technique with a large field of view and high spatial resolution, which is also useful for characterizing the wavefront of an x-ray probe. The performance of this technique is degraded by positioning errors due to the drift between the sample and illumination optics. We propose an experimental approach for correcting the positioning errors and demonstrate success by two-dimensionally reconstructing both the wavefront of the focused x-ray beam and the complex transmissivity of the weakly scattering objects at the pixel resolution of better than 10 nm in the field of view larger than 5 μm. This method is applicable to not only the observation of organelles inside cells or nano-mesoscale structures buried within bulk materials but also the characterization of probe for single-shot imaging with x-ray free electron lasers. © 2011 American Physical Society.Yukio Takahashi, Akihiro Suzuki, Nobuyuki Zettsu, Yoshiki Kohmura, Yasunori Senba, Haruhiko Ohashi, Kazuto Yamauchi, and Tetsuya Ishikawa. Phys. Rev. B 83(21), 214109 (2011)

Microstitching interferometer and relative angle determinable stitching interferometer for half-meter-long X-ray mirror

Haruhiko Ohashi, Takashi Tsumura, Hiromi Okada, Hidekazu Mimura, Tatsuhiko Masunaga, Yasunori Senba, Shunji Goto, Kazuto Yamauchi, and Tetsuya Ishikawa "Microstitching interferometer and relative angle determinable stitching interferometer for half-meter-long x-ray mirror", Proc. SPIE 6704, Advances in Metrology for X-Ray and EUV Optics II, 670405 (1 October 2007); https://doi.org/10.1117/12.733476

Damage characteristics of platinum/carbon multilayers under X-ray free-electron laser irradiation

Jangwoo Kim, Takahisa Koyama, Hirokatsu Yumoto, Ayaka Nagahira, Satoshi Matsuyama, Yasuhisa Sano, Makina Yabashi, Haruhiko Ohashi, Tetsuya Ishikawa, and Kazuto Yamauchi "Damage characteristics of platinum/carbon multilayers under x-ray free-electron laser irradiation", Proc. SPIE 8848, Advances in X-Ray/EUV Optics and Components VIII, 88480S (27 September 2013); https://doi.org/10.1117/12.2022735

Measurement of the X-ray spectrum of a free electron laser with a wide-range high-resolution single-shot spectrometer

We developed a single-shot X-ray spectrometer for wide-range high-resolution measurements of Self-Amplified Spontaneous Emission (SASE) X-ray Free Electron Laser (XFEL) pulses. The spectrometer consists of a multi-layer elliptical mirror for producing a large divergence of 22 mrad around 9070 eV and a silicon (553) analyzer crystal. We achieved a wide energy range of 55 eV with a fine spectral resolution of 80 meV, which enabled the observation of a whole SASE-XFEL spectrum with fully-resolved spike structures. We found that a SASE-XFEL pulse has around 60 longitudinal modes with a pulse duration of 7.7 ± 1.1 fs.Inubushi, Y.; Inoue, I.; Kim, J.; Nishihara, A.; Matsuyama, S.; Yumoto, H.; Koyama, T.; Tono, K.; Ohashi, H.; Yamauchi, K.; Yabashi, M. Measurement of the X-ray Spectrum of a Free Electron Laser with a Wide-Range High-Resolution Single-Shot Spectrometer. Appl. Sci. 2017, 7, 584. https://doi.org/10.3390/app7060584

Damage to inorganic materials illuminated by focused beam of X-ray free-electron laser radiation

X-ray free-electron lasers (XFELs) that utilize intense and ultra-short pulse X-rays may damage optical elements. We investigated the damage fluence thresholds of optical materials by using an XFEL focusing beam that had a power density sufficient to induce ablation phenomena. The 1 μ4m focusing beams with 5.5 keV and/or 10 keV photon energies were produced at the XFEL facility SACLA (SPring-8 Angstrom Compact free electron LAser). Test samples were irradiated with the focusing beams under normal and/or grazing incidence conditions. The samples were uncoated Si, synthetic silica glass (SiO2), and metal (Rh, Pt)-coated substrates, which are often used as X-ray mirror materials.Takahisa Koyama, Hirokatsu Yumoto, Kensuke Tono, Tadashi Togashi, Yuichi Inubushi, Tetsuo Katayama, Jangwoo Kim, Satoshi Matsuyama, Makina Yabashi, Kazuto Yamauchi, and Haruhiko Ohashi "Damage to inorganic materials illuminated by focused beam of x-ray free-electron laser radiation", Proc. SPIE 9511, Damage to VUV, EUV, and X-ray Optics V, 951107 (12 May 2015); https://doi.org/10.1117/12.218277

Realization of a scanning soft X-ray microscope for magnetic imaging under high magnetic fields

For the purpose of imaging element- and shell-specific magnetic distributions under high magnetic fields, a scanning soft X-ray microscope has been developed at beamline BL25SU, SPring-8, Japan. The scanning X-ray microscope utilizes total electron yield detection of absorbed circularly polarized soft X-rays in order to observe magnetic domains through the X-ray magnetic circular dichroism effect. Crucially, this system is equipped with an 8 T superconducting magnet. The performance and features of the present system are demonstrated by magnetic domain observations of the fractured surface of a Nd₁₄.₀Fe₇₉.₇Cu₀.₁B₆.₂ sintered magnet.Y.Kotani, Y.Senba, K.Toyoki, et al. Realization of a scanning soft X-ray microscope for magnetic imaging under high magnetic fields. Journal of Synchrotron Radiation 25, 1444 (2018); https://doi.org/10.1107/S1600577518009177