Nearly diffraction-limited X-ray focusing with variable-numerical-aperture focusing optical system based on four deformable mirrors.

Satoshi Matsuyama,Takashi Kimura,Yasuhisa Sano,Hiroki Nakamori,Takumi Goto,Makina Yabashi,Kazuto Yamauchi,Yoshinori Nishino,Krishna P Khakurel,Tetsuya Ishikawa,Yoshiki Kohmura

doi:10.1038/srep24801

Satoshi Matsuyama, Takashi Kimura + Show 9 more

Open Access

https://doi.org/10.1038/srep24801

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Abstract

Unlike the electrostatic and electromagnetic lenses used in electron microscopy, most X-ray focusing optical systems have fixed optical parameters with constant numerical apertures (NAs). This lack of adaptability has significantly limited application targets. In the research described herein, we developed a variable-NA X-ray focusing system based on four deformable mirrors, two sets of Kirkpatrick–Baez-type focusing mirrors, in order to control the focusing size while keeping the position of the focus unchanged. We applied a mirror deformation procedure using optical/X-ray metrology for offline/online adjustments. We performed a focusing test at a SPring-8 beamline and confirmed that the beam size varied from 108 nm to 560 nm (165 nm to 1434 nm) in the horizontal (vertical) direction by controlling the NA while maintaining diffraction-limited conditions.

Highlights

Downstream mirror aperture is substituted with two deformable mirrors[14,15,16,17,18] arranged in the KB configuration, it is possible to transmit the full incident flux to the final focus
We proposed a variable-NA focusing system based on four deformable mirrors[21,22,23], which is quite different from optical systems that can shape X-rays at the level of a few tens of microns or a few microns[24]
To illustrate the relationship between the NAs and the full widths at half-maximum (FWHMs) of the focused beam, Fig. 7 shows the calculated and experimentally measured FWHMs plotted against the aperture ratio

Summary

Introduction

Downstream mirror aperture is substituted with two deformable mirrors[14,15,16,17,18] arranged in the KB configuration, it is possible to transmit the full incident flux to the final focus. It is technically challenging to fabricate high-quality deformable mirrors to achieve diffraction-limited focusing: the error between the figure and the ideal shape should be smaller than λ , where λ and θ are the wavelength and grazing incidence angle, respectively. When λ = 0.124 nm and θ = 8 4simn θrad, the maximum error to be accepted is ~4 nm This severe requirement has caused substantial difficulty in achieving X-ray nanofocusing with deformable mirrors. To overcome these problems, we developed a high-quality deformable mirror based on piezoelectric elements[18,19,20]. The focused beams, characterized by the knife-edge scanning method, were successfully changed by adjusting only the NA while satisfying the diffraction-limited condition

Methods

Results

Conclusion