Fabrication of soft x-ray monolithic Wolter mirror based on surface scanning measurement using touch probe

Ultracompact mirror device for forming 20-nm achromatic soft-X-ray focus toward multimodal and multicolor nanoanalyses

Nanoscale soft-X-ray microscopy is a powerful analysis tool in biological, chemical, and physical sciences. To enhance its probe sensitivity and leverage multimodal soft-X-ray microscopy, precise achromatic focusing devices, which are challenging to fabricate, are essential. Here, we develop an ultracompact Kirkpatrick-Baez (ucKB) mirror, which is ideal for the high-performance nanofocusing of broadband-energy X-rays. We apply our advanced fabrication techniques and short-focal-length strategy to realize diffraction-limited focusing over the entire soft-X-ray range. We achieve a focus size of 20.4 nm at 2 keV, which represents a significant improvement in achromatic soft-X-ray focusing. The ucKB mirror extends soft-X-ray fluorescence microscopy by producing a bicolor nanoprobe with a 1- or 2-keV photon energy. We propose a subcellular chemical mapping method that allows a comprehensive analysis of specimen morphology and the distribution of light elements and metal elements. ucKB mirrors will improve soft-X-ray nanoanalyses by facilitating photon-hungry, multimodal, and polychromatic methods, even with table-top X-ray sources.

Soft-X-ray nanobeams formed by aberration-reduced elliptical mirrors with large numerical aperture

X-ray focusing mirrors often employ the Kirkpatrick-Baez (KB) geometry, which sequentially crosses two elliptic-cylindrical mirrors in grazing-incidence configurations. However, KB mirrors do not satisfy the Abbe sine condition and thus potentially expand the focus size with severe coma aberration. Satisfying the Abbe sine condition complicates mirror shapes or increases the number of ultraprecision mirrors required. The present study shows that the focal length and mirror length of KB mirrors have to be shortened to simultaneously achieve a large numerical aperture and reduced aberration. Such ultracompact KB (ucKB) mirrors are examined using a simulation that combines ray tracing and wave propagation. The focus intensity distributions show that ucKB mirrors suppress the aberration produced by their rotation errors and that they robustly achieve diffraction-limited focusing. The simulation results are confirmed in a synchrotron radiation experiment. ucKB mirrors can be advantageous for soft-X-ray nanoprobes, which require focusing devices to achieve a large numerical aperture.

Design and preliminary evaluation of a multi-channel multi-energy point integrated Wolter microscope

In inertial confinement fusion, high-precision x-ray imaging is crucial for understanding the states of matter under extreme conditions. To observe the target asymmetry during compression, multiple imaging spots with varying energy responses are necessary. However, integrating multiple imaging channels in a grazing incidence x-ray imaging scheme is challenging, and there is an urgent need for effective combination of multi-color and high-throughput diagnostics. This study presents a design method for a multi-channel integrated Wolter microscope with high spatial resolution, wide-band response, and high throughput. The basic optical configuration, adjustment method, and multi-channel integration scheme are discussed in detail. A 10 keV-class three-channel integrated Wolter microscope is proposed for verification, with an estimated spatial resolution better than 4.0 µm in a field of view of ±500µm. The peak response efficiencies for each imaging channel are calculated as 5.2×10-5 s r, 8.6×10-5 s r, and 2.2×10-4 s r, respectively.