Ellipsoidal mirror for two-dimensional 100-nm focusing in hard X-ray region

Abstract

Cutting-edge hard X-ray microscopy strongly depends on sophisticated focusing optics and ultrabright X-ray sources at synchrotron-radiation and X-ray free-electron laser (XFEL) facilities. These facilities typically provide two-dimensional nanofocusing X-ray beams by combining one-dimensional focusing mirrors. However, single-reflecting two-dimensional focusing mirrors with an ellipsoidal surface, which are well-known to possess high efficiency, have limited microfocusing applications. In this paper, we present an ultrahigh-precision ellipsoidal mirror for two-dimensional X-ray nanofocusing by overcoming the difficulties faced in the manufacturing process of its aspherical surface, including the surface-processing methods and surface metrology. The developed mirror has nanoscale accuracy, and it achieves focus size of 85 nm × 125 nm (full width at half maximum) using 7-keV X-rays. Two-dimensional focus was demonstrated in the same focal plane by resolving 50-nm test structures by scanning X-ray microscopy using a focusing beam. These achievements represent an important first step toward realizing two-dimensional aspherical mirrors with complex designs, in addition to ultralow loss and unprecedented small focusing property for extensive optical applications in synchrotron-radiation and XFEL facilities as well as in other scientific fields that require ultraprecision optical surfaces.

Derivation of closed-form ellipsoidal X-ray mirror shapes from Fermat's principle

“…With sagittal curvature, a single ellipsoidal mirror can be used for two-dimensional focusing in either an off-axis configuration [Fig. 1(b)] (Yumoto et al, 2017) or on-axis, with an annular shape [Fig. 1(a)] (Takeo et al, 2020).…”

High-fluence and high-gain multilayer focusing optics to enhance spatial resolution in femtosecond X-ray laser imaging

“…Highly efficient ellipsoidal multilayer mirrors 44 may further increase the fluence with ~100 nm focusing by twofold or more by using identical horizontal and vertical focal spot sizes and enhancing the reflectivity with a single reflection, although further technical developments are necessary. In addition, it is desired to increase the focusing fluence by improving XFEL sources in terms of the pulse energy and incident XFEL beam profile.…”

Optical considerations and ray tracing simulation of an open-type Wolter microscope for implosion imaging diagnostics

“…This bottleneck is preventing the advancement of Wolter microscope techniques. There are many modern polishing methods that can be employed for mirror forming, and elastic emission machining is one of them that can achieve precise material removal at the atom level [8] . Due to the utilization of modern ultraprecision polishing methods, the shape and roughness of the mirror surface can be significantly improved.…”