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

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.

Generation of apodized X-ray illumination and its application to scanning and diffraction microscopy

“…All of the mirrors were fabricated in an ultra-precise manner such that the wavefront distortion by the surface roughness is smaller than that required by the Rayleigh criterion for ideal focusing. For the mirrors used in the system, the Rayleigh criterion requires the surface roughness to be less than 4 nm while the measured value is $ 2 nm (Matsuyama et al, 2016). It is known that a single elliptical KB mirror system causes comatic aberration.…”

“…However, when using two sets of KB mirror systems in the (+, À) configuration, the Abbe sine condition is satisfied and the comatic aberration can be removed. A detailed explanation of the alignment and deformation process of the two-stage deformable KB mirror system is discussed elsewhere (Matsuyama et al, 2016).…”

Extremum seeking x-ray position feedback using power line harmonic leakage as the perturbation

“…(1) using Eqs. (2) and (9). When the random beam position motion is slow (ω ≪ λ), the feedback maintains alignment.…”

“…Synchrotron radiation is a powerful tool that has been used to explore the structural [1][2][3], electronic [4][5][6], and chemical [7] properties of both organic and inorganic materials. In recent years, the promise of nanoscience for new exciting technologies has motivated the development of x-ray optics that can better resolve nanoscale phenomena [8][9][10]. While x-ray optics and synchrotron instrumentation have seen tremendous progress, beam stabilization methods have received less attention.…”

Using refractive optics to broaden the focus of an X-ray mirror

“…Existing methods for increasing the focus size include changing the surface profile of a bimorph mirror in order to change the mirror focal length , using a combination of variable focus mirrors or compound refractive lenses to achieve a zoom configuration (Matsuyama et al, 2016;Evans et al, 2007;Schneider et al, 2013) or using slits to change the size of the secondary source (Fischetti et al, 2013). The first method is simple to implement but is liable to producing caustic-like structures on the focal spot (Sutter et al, 2014).…”