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Development of Electroformed X-ray Optics Bridging Synchrotron Technology and Space Astronomy

Ryuto Fujii, Koki Sakuta, Kazuki Ampuku, Yusuke Yoshida, Makoto Yoshihara, Ayumu Takigawa, Keitoku Yoshihira, Tetsuo Kano, Naoki Ishida, Noriyuki Narukage, Keisuke Tamura, Kikuko Miyata, Gota Yamaguchi, Hidekazu Takano, Yoshiki Kohmura, Shutaro Mohri, Takehiro Kume, Yusuke Matsuzawa, Yoichi Imamura, Takahiro Saito, Kentaro Hiraguri, Hirokazu Hashizume, Hidekazu Mimura, Ikuyuki Mitsuishi

Abstract

We have developed X-ray telescope mirrors using an original electroforming replication technique established through the fabrication of millimeter-aperture, ultra-short-focal-length nanofocusing mirrors for synchrotron X-ray microscopy. This paper presents detailed results of X-ray illumination tests of a 60-mm-diameter, full-circumference, double-reflection monolithic electroformed nickel mirror and its Mirror Module Assembly (MMA). The experiments were conducted at the 1-km beamline BL29XUL at SPring-8. To simulate a parallel X-ray beam from celestial sources, we constructed a dedicated evaluation system, the High-Brilliance X-ray Kilometer-long Large-Area Expanded-beam Evaluation System (HBX-KLAEES). Owing to the high photon flux and the quasi-point-like source with a small divergence provided by HBX-KLAEES, the imaging performance was evaluated with high fidelity, resolving both the sharp core and large-angle components of the Point Spread Function (PSF). The results show an extremely sharp core with a Full Width at Half Maximum (FWHM) of 0.7 arcsec and a Half Power Diameter (HPD) of 14 arcsec, even after integration into the MMA. In addition, a positive correlation was found between angular resolution and axial figure error in both the primary and secondary mirror sections, indicating that axial figure errors contribute to image degradation. Based on these results, the MMA was selected as one of the hard X-ray optics for the FOXSI-4 sounding rocket experiment, which performs high-resolution soft and hard X-ray imaging spectroscopy of solar flares and was successfully launched. These results demonstrate the potential for further improvements in angular resolution and the development of high-resolution, ultra-short focal length X-ray optics for small satellites, including CubeSats.

Development of Electroformed X-ray Optics Bridging Synchrotron Technology and Space Astronomy

Abstract

We have developed X-ray telescope mirrors using an original electroforming replication technique established through the fabrication of millimeter-aperture, ultra-short-focal-length nanofocusing mirrors for synchrotron X-ray microscopy. This paper presents detailed results of X-ray illumination tests of a 60-mm-diameter, full-circumference, double-reflection monolithic electroformed nickel mirror and its Mirror Module Assembly (MMA). The experiments were conducted at the 1-km beamline BL29XUL at SPring-8. To simulate a parallel X-ray beam from celestial sources, we constructed a dedicated evaluation system, the High-Brilliance X-ray Kilometer-long Large-Area Expanded-beam Evaluation System (HBX-KLAEES). Owing to the high photon flux and the quasi-point-like source with a small divergence provided by HBX-KLAEES, the imaging performance was evaluated with high fidelity, resolving both the sharp core and large-angle components of the Point Spread Function (PSF). The results show an extremely sharp core with a Full Width at Half Maximum (FWHM) of 0.7 arcsec and a Half Power Diameter (HPD) of 14 arcsec, even after integration into the MMA. In addition, a positive correlation was found between angular resolution and axial figure error in both the primary and secondary mirror sections, indicating that axial figure errors contribute to image degradation. Based on these results, the MMA was selected as one of the hard X-ray optics for the FOXSI-4 sounding rocket experiment, which performs high-resolution soft and hard X-ray imaging spectroscopy of solar flares and was successfully launched. These results demonstrate the potential for further improvements in angular resolution and the development of high-resolution, ultra-short focal length X-ray optics for small satellites, including CubeSats.
Paper Structure (16 sections, 9 figures, 1 table)

This paper contains 16 sections, 9 figures, 1 table.

Table of Contents

  1. Introduction
  2. Sample
  3. Mirror
  4. Mirror Module Assembly (MMA)
  5. X-ray Illumination Tests
  6. Experimental Setup
  7. Spot-scan Method
  8. Full-illumination Method (HBX-KLAEES)
  9. Detector System
  10. Imaging Performance
  11. Alignment of Optical Axis and Focal Adjustment
  12. Analysis and Results
  13. Spot-scan Test of the Single Mirror
  14. Full-illumination Test for the MMA Using HBX-KLAEES
  15. Discussion
  16. ...and 1 more sections

Figures (9)

  • Figure 1: Electroformed X-ray mirror (left), schematic of the MMA design (center), and photograph of the MMA (right).
  • Figure 2: Experimental setup inside the fourth experimental hutch of SPring-8 beamline BL29XUL. The arrow indicates the direction of incident X-ray photons from the upstream side. The setup consists of a vacuum duct, sample, sample stage, detector, and detector stage. The coordinate axes are also defined in the figure.
  • Figure 3: Conceptual diagram of the High-Brilliance X-ray Kilometer-long Large-Area Expanded-beam Evaluation System (HBX-KLAEES) constructed at SPring-8 beamline BL29XUL. The distance from the virtual point source to the sample is approximately 1 km, enabling highly collimated beam conditions.
  • Figure 4: Left : example of X-ray images acquired from local illumination regions of the mirror using the spot-scan method at 12 keV. Images at phase angles of 0${}^\circ$ (upper left), 90${}^\circ$ (upper right), 180${}^\circ$ (lower left), and 270${}^\circ$ (lower right) are shown. Right : same as Figure left panels, but showing the PSF and EEF profiles.
  • Figure 5: Azimuthal dependence of the angular resolution (HPD) of the mirror obtained using the spot-scan method at 12 keV.
  • ...and 4 more figures