High-speed imaging is used to directly visualize various phenomena in material processing such as cutting, electric discharge machining, and laser machining. By using high energy X-rays, phenomena inside materials can be analyzed. In this study, the phenomena of metal drilling were observed using a high-speed imaging system with 100 keV X-rays at SPring-8. Various interesting movies were observed with sub-millisecond order time resolution. In this presentation, we will show the latest results of this research and explain the importance of X-ray high speed imaging in the fields of materials processing.
In the soft x-ray region, the demand for focusing x-rays into a spot of nanometer order size with high efficiency has been increasing. Ellipsoidal and Wolter mirrors, which are representative of ideal reflective focusing optics for soft x-rays, have optical advantages such as achromaticity, large acceptance, high efficiency and high numerical aperture, which are suitable to fully utilize the next-generation synchrotron light sources. Recently, the fabrication process of soft x-ray mirrors of replication type using nickel electroforming was developed, and several focusing experiments with ellipsoidal and Wolter mirrors were reported. The experimental environment of these mirrors, however, was limited due to the magnetism of the nickel body. We are currently developing the diamagnetic mirror fabrication process using copper electroforming technique to expand its application. In order to prevent oxidization of the replicated surface, this study demonstrates electroforming of copper mirror that has the reflective surface of gold. The surface roughness replicated from a flat substrate was 0.321 nm in root-mean-square in 0.1 mm × 0.1 mm area. The circularity of the gold inner surface of a copper electroformed mirror was evaluated at 26 nm in peak-to-valley.
Wolter mirrors work as imaging optics of X-ray telescopes. We have been developing a Wolter mirror for the FOXSI-4 project in 2023 using a high-precision Ni electroforming process. The figure accuracy of mirrors is one of the main factors determining the spatial resolution in X-ray imaging. In this study, we optimized the electrodeposition conditions from the viewpoint of the uniformity of film thickness. The simulation model was developed to correctly predict the film thickness distribution before fabrication, whose parameters and boundary conditions were determined through electrochemical experiments. The model calculates the distribution of current density on the surface of the cathode by finite element analysis. In this paper, we report the current status of the electroforming process specializing in Wolter mirrors in X-ray telescopes.
For many years, Wolter mirrors have been used as imaging elements in X-ray telescopes. The shape error of Wolter mirrors fabricated by replicating the shape of a mandrel originates from the replication error in electroforming. We have been developing an X-ray focusing mirror for synchrotron radiation X-rays, as well as a high-precision electroforming process. In this paper, we report on the application of the advanced electroforming process to the fabrication of Wolter mirrors for the FOXSI Sun observation project. We also discuss the figuring accuracy of the mandrel.
We had been developing replicated aluminum foil optics for previous missions such as ASCA, Suzaku, and, Hitomi. This sort of X-ray optics can be lighter but the angular resolution is limited to on the order of arcminutes. Thus, to improve the angular resolution with light performances, we have started developing electro formed X-ray optics. Electroforming is a technology that can transfer to a substrate with high accuracy by plating the nano-level structure of a super-precision master and makes it easier to fabricate Wolter type-I shaped two-stage full-shell mirrors.
Electroforming replication is an essential technique for fabricating full-shell, grazing-incidence mirrors for use in space, laboratories, and synchrotron experiments. For X-ray astronomy, a nickel electroforming replication process was developed and is used to produce lightweight and high-resolution X-ray mirrors. In addition, the electroforming process for fabricating X-ray mirrors for use in synchrotron experiments has undergone remarkable development over the past decade. We expect that the use of the ground-based electroforming replication process for the production of optics for Xray astronomy will lead to further improvements in the performance of X-ray telescopes. This paper describes our ongoing development efforts in the nickel-electroforming replication process, including the results of a pilot study.
Since a replication-type of the Wolter mirror is obtained as the negative shape of its mandrel via shape replication represented by electroforming, a high precision mandrel fabrication process is essential for nano-focusing with the mirror at synchrotron radiation facilities. In particular, three-dimensional shape measurement technique for the mandrel is required. In this study, we developed the high precision three-dimensional shape measurement system dedicated for the Wolter mandrels. First, the shape error distributions of the ellipsoidal surface and the hyperboloid surface were measured independently. The geometrical relation between the surfaces was constrained by the longitudinal profiles which include the intersection measured by a profilometer. The diameter was also measured and finally the three-dimensional shape distribution was obtained. Applying this system, we fabricated a high precision Wolter mandrel.
This paper presents the designs and simulations of twin Wolter mirrors for focusing and imaging experiments with soft Xray free electron lasers. Wave-optical simulations at a photon energy of 100 eV indicate that the designed focusing Wolter mirror focuses soft X-ray beams to a 300 nm × 200 nm spot with an acceptable rotational error of 1.7 mrad × 1.4 mrad and that the objective Wolter mirror, which receives the beam that passes through the focusing Wolter mirror and a sample, forms bright-field images with a spatial resolution of 140 nm × 140 nm. The focusing Wolter mirror enables long-term experiments with high stability, and the objective Wolter mirror is applicable to imaging-before-destruction.
An ellipsoidal mirror is a soft X-ray reflective focusing device. We are developing precise ellipsoidal mirrors based on an electroforming process. To improve the fabrication process, three-dimensional shape measurements with a high accuracy are required. In this research we develop a method to measure ellipsoidal shapes by industrial X-ray computed tomography (CT). The X-ray CT process consists of measuring the mirror shape and determining the parameters of the ellipsoid. We also evaluate the reproducibility of X-ray CT measurements and clarify that the accuracy is at the 5-m level.
Ellipsoidal mirrors are ideal focusing optics for soft x-rays because of advantages that include high numerical aperture, high efficiency, and no chromatic aberrations. Shape accuracy of nanometer order is required on the internal surface of a mirror with a diameter of around 10 mm. Because of the difficulty of processing the internal surface, ellipsoidal mirrors are fabricated by replication of the shapes of master mandrels. In previous studies, a fabrication process was developed for x-ray ellipsoidal mirrors involving mandrel fabrication and nickel electroforming. 40-mm-long ellipsoidal mirrors were fabricated and a focused beam with full width at half maximum (FWHM) of 240 nm was obtained. For better focusing performance and expansion of the applicable energy range, we designed and fabricated a 120-mm-long ellipsoidal mirror from the master mandrel with a shape accuracy of 3.8 nm (root mean square). A focusing experiment was also performed at the synchrotron radiation facility, SPring-8 (BL25SU). A focused beam with FWHM of 1 μm was obtained.
An X-ray ellipsoidal mirror requires nanometer-level shape accuracy for its internal surface. Owing to the difficulty in processing the surface, electroforming using a high precision master mandrel has been applied to mirror fabrication. In order to investigate the replication accuracy of electroforming, a measurement method for the entire internal surface of the mirror must be developed. The purpose of this study is to evaluate the shape replication accuracy of electroforming. In this study, a three-dimensional shape measurement apparatus for an X-ray ellipsoidal mirror is developed. The apparatus is composed of laser probes, a contact probe, reference flats, a z-axis stage, and a rotation table. First, longitudinal profiles of a mandrel or mirror placed vertically on the rotation table are measured at several angular positions. Subsequently, without realignment of the measured sample, circularity at every height is measured at regular intervals of 0.1 mm. During each measurement, the effect of motion errors is calculated and subtracted from each profile by referring to the distances between the probes and reference flats. Combining the circularity data with the longitudinal profiles, a three-dimensional error distribution of the entire surface is obtained. Using a mandrel with nanometer-level shape accuracy and a replicated mirror, the performance of the measurement apparatus and the replication accuracy are evaluated. Measurement repeatability of single-nanometer order and replication accuracy of sub-100-nm order are confirmed.
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