The atmospheric characterization of habitable candidates is one of the effective approaches for search for life out of the solar system. However, it is much hard by high planet-star flux contrast, 10-8 - 10-10 . A coronagraphic mask proposed by Itoh & Matsuo (2020) can suppress host stellar light but is imposed by a strict wavelength range limit of 0.3%. A spectroscopic coronagraph that combines the diffraction-limited coronagraph with a spectrograph is expected to achieve enlarges the effective bandwidth. On the other hand, a non-common path error, which is induced by the spectrograph, could limit the achievable contrast. We designed a high-accuracy spectrograph motivated for the spectroscopic coronagraph and measured its wavefront error. The common path error is 9.9 nm RMS, which is mostly caused by the alignment error between the convex grating and spherical mirror of the spectrograph. The achievable contrast of the spectroscopic coronagraph was also estimated from the non-common path error measurement. We found that the contrast of 10-8 could be achieved with a bandwidth of 5%, which is a promising result as the first step.
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.
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