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.
The Wolter mirror is a promising imaging device for soft x-ray microscopy owing to its excellent characteristics. Its annular aperture enables high-NA design while maintaining high photon transfer efficiency. However, its deep and narrow cylinder-like shape makes its fabrication difficult. Despite its long history, the Wolter mirror has not been practically used for high-resolution microscopy. We have been developing a fabrication process for grazing incidence mirrors with rotationally symmetric shapes. The mirrors are replicated from precisely machined mandrels. We employ electroforming as a replication method with high replication accuracy and reproductivity. Here, we report the first fabrication of a Wolter mirror and discuss the replication quality in electroforming. The imaging quality of Wolter mirror is also evaluated in an observation experiment using a visible-light microscope.
Mirrors are key devices for creating various systems in optics. Focusing X-ray and extreme ultraviolet (EUV) light requires mirror surfaces with an extremely high accuracy. The figure of an ellipsoidal mirror is obtained by rotating an elliptical profile, and using such a mirror, soft X-ray and EUV light can be focused to dimensions on the order of nanometers without chromatic aberration. Although the theoretical performance of ellipsoidal mirrors is extremely high, the fabrication of an ideal ellipsoidal mirror remains problematic. Based on this background, we have been working to develop a fabrication system for ellipsoidal mirrors. In this proceeding, we briefly introduce the fabrication process and the soft X-ray focusing performance of the ellipsoidal mirror fabricated using the proposed process.
Ellipsoidal mirrors are one of the most promising types of X-ray mirror, because the mirror can focus X-rays to
nanometer size with a large aperture and no chromatic aberration. However, so far ideal ellipsoidal mirrors cannot be
realized by any manufacturing methods. One of the reasons is there is no fabrication method to process their inside
surface with a diameter of several millimeters with nanometer-level accuracy. We propose and develop a manufacturing
process of the ellipsoidal mirror. First, a master which has the reversed shape is prepared using grinding, polishing and
Elastic Emission Machining (EEM). EEM can finish the surface shape to within 2nm (RMS). Then, the ellipsoidal mirror
is produced by replicating the surface using an electroforming deposition method. By conducting the process without any
stress at room temperature, replicating the surface roughness and shape with nanometer order accuracy is possible. In
this paper, we report the current status of manufacturing of the ellipsoidal mirror.