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This study presents an approach for fabricating Wolter type-I mirrors for x-ray telescopes using a nickel electroforming replication process with quartz glass mandrels. The proposed method addresses the challenges encountered in conventional fabrication techniques, which involve using electroless nickel-coated aluminum mandrels that are susceptible to corrosion and thermal deformation. Quartz glass mandrels offer excellent chemical, thermal, and mechanical stability, enabling the efficient production of high-performance mirrors. Wolter type-I mirrors for telescopes possess a large aperture that collects x-ray photons from the universe. However, previous nickel electroforming replication processes using quartz glass mandrels have challenges in fabricating large mirrors, particularly due to bubble pit formation during nickel shell development. In this study, we introduced an efficient pitting inhibition technique via vacuum degassing. This technique facilitates the precise replication of pit-free Wolter type-I mirrors for telescopes using quartz glass mandrels. We demonstrated the fabrication process on a Wolter type-I mirror proposed for FOXSI-4 [(FOXSI) Focusing Optics X-ray Solar Imager], resulting in three mirrors obtained from the same mandrel without repolishing or repairing. The figure error of the mirror was within 1 µm over most areas in both longitudinal and circumferential directions. The ray-tracing simulation indicated that the performance of the mirror was ∼12 arcsec in half-power diameter, comparable to the performance achieved by previous high-resolution x-ray missions. [ABSTRACT FROM AUTHOR]

In this study, figure correction of a master mandrel of a Wolter mirror by organic abrasive machining (OAM) was demonstrated. In OAM, a flow of slurry, dispersed with organic particles, locally removes the surface of a workpiece in contact with a rotating machining tool. A computer-controlled machining system was used to perform the selective removal of a fused silica surface at a spatial resolution of 200 µm. A master mandrel of a Wolter mirror for soft x-ray microscopes was fabricated with a figure accuracy of <1 nm root mean square, which is sufficient for diffraction-limited imaging at a wavelength of 10 nm. [ABSTRACT FROM AUTHOR]

The monolithic Wolter mirror is an ideal optical device for focusing soft x rays to a submicron-sized spot, with the advantages of high efficiency, large acceptance, achromaticity, and robustness to alignment error. The fabrication process for this type of mirror has not been established because of the difficulty in highly accurate figure measurement of free-form surfaces with small radii of curvature and steep profiles. In this study, we employed tactile scanning measurement for surface characterization to fabricate a high-precision Wolter mirror. First, it was demonstrated that the touch probe measurement did not leave scratches on the raw surface of the mirror substrate. Next, the measurement capability of the surface profiler was assessed, and the data analysis conditions were determined. Finally, the Wolter mirror was fabricated through repeated figure correction based on the tactile measurement, and the figure error of the final surface was evaluated. Wave-optical simulations that used this error as reference suggested that the size of the beam focused by the mirror was equivalent to the theoretical value at 1000 eV. The reflected image with uniform intensity distribution obtained at SPring-8 also revealed the effectiveness of the present fabrication approach based on tactile measurement. [ABSTRACT FROM AUTHOR]

We developed a copper electroforming replication (CER) process to fabricate precise ellipsoidal mirrors for soft x-ray focusing. Some applications of ellipsoidal mirrors in x-ray microscopy require that all components that are close to samples, including the mirrors, are made of non-magnetic materials. In this study, a non-magnetic copper ellipsoidal mirror was fabricated by replicating a figured and super-polished quartz glass mandrel using an electroforming technique. It was found that the CER process has a high replication accuracy of 8 nm. The focusing performance of the mirror was characterized using a soft x-ray free-electron laser with a photon energy of 100 eV. A small focus size of 370 × 400 nm2 was achieved with a high reflectivity of 65%. [ABSTRACT FROM AUTHOR]

The focusing of x rays is essential in various types of x-ray microscopy because the size and flux of the illuminating beam determine the spatial resolution and signal intensity, respectively. A system with grazing incidence mirrors allows highly efficient x ray focusing with beam dimensions on the nanometer scale. Tube-shaped mirrors with a large numerical aperture and high demagnification, including ellipsoidal mirrors and Wolter mirrors, have recently been developed for soft x-ray nanofocusing. However, these mirrors have low efficiency because they cannot focus the central part of the illumination beam. Here, we propose a two-stage focusing system, in which a ring-shaped beam formed by a ring-focusing mirror illuminates a quasi-Wolter mirror. A prototype of the system is experimentally constructed at beamline BL25SU-A of SPring-8. Observation of the wavefront error based on ptychography enables efficient alignment of the two mirrors. Using this alignment procedure, we achieve a spot size of less than 200 nm at 300 eV. [ABSTRACT FROM AUTHOR]

Ellipsoidal mirrors are promising optical devices for soft x-ray focusing. A fabrication process consisting of master fabrication and replication has been developed to produce ellipsoidal mirrors with wide apertures of approximately 10 mm. In the present study, the focusing performance of an ellipsoidal mirror was evaluated using soft x-rays in the soft x-ray beamline BL25SU-a of SPring-8. The focus sizes were measured at photon energies of 300, 400, and 500 eV. A quantitative figure error of the ellipsoidal mirror was also evaluated by analyzing the wavefield of the focused beam retrieved using ptychography. The figure error distributions measured at different photon energies agreed with each other at a root mean square level of 1 nm. The developed focusing system can be used for various types of microscopy, allowing the use of a wide range of x-ray energies. [ABSTRACT FROM AUTHOR]

An x-ray ellipsoidal mirror is an ideal tool for focusing soft x-rays. Because nanometer-level shape accuracy is required in the internal surface of a mirror having a small diameter, it is difficult to fabricate the mirror by processing the surface directly. We developed a fabrication process for soft x-ray ellipsoidal mirrors in which the surface of a high-precision quartz mandrel with the inverted shape of the designed mirror is replicated by nickel sulfamate electroforming. In this study, an ellipsoidal mirror of 40-mm length was fabricated and the shape accuracy of the replicated surface was evaluated by a measurement method using a contact probe. The root mean square (RMS) of the replication error in the entire measured surface was 27.2 nm. When the evaluated area was half the replicated surface near the middle of the mirror, the RMS of the replication error was 14.7 nm. Wave-optical simulation suggested that it is possible to focus soft x-rays to a spot with a diameter of 400 nm. [ABSTRACT FROM AUTHOR]

In X-ray focusing, grazing incidence mirrors offer advantages of no chromatic aberration and high focusing efficiency. Although nanofocusing mirrors have been developed for the hard X-ray region, there is no mirror with nanofocusing performance in the soft X-ray region. Designing a system with the ability to focus to a beam size smaller than 100 nm at an X-ray energy of less than 1 keV requires a numerical aperture larger than 0.01. This leads to difficulties in the fabrication of a soft X-ray focusing mirror with high accuracy. Ellipsoidal mirrors enable soft X-ray focusing with a high numerical aperture. In this study, we report a production process for ellipsoidal mirrors involving mandrel fabrication and replication processes. The fabricated ellipsoidal mirror was assessed under partial illumination conditions at the soft X-ray beamline (BL25SU) of SPring-8. A focal spot size of less than 250 nm was confirmed at 300 eV. The focusing tests indicated that the proposed fabrication process is promising for X-ray mirrors that have the form of a solid of revolution, including Wolter mirrors. [ABSTRACT FROM AUTHOR]