Methodology for optimalin situalignment and setting of bendable optics for nearly diffraction-limited focusing of soft x-rays

Abstract

Abstract. We demonstrate a comprehensive and broadly applicable methodology for the optimal in situ configuration of bendable soft x-ray Kirkpatrick-Baez mirrors. The mirrors used for this application are preset at the Advanced Light Source Optical Metrology Laboratory prior to beamline installation. The in situ methodology consists of a new technique for simultaneously setting the height and pitch angle of each mirror. The benders of both mirrors were then optimally tuned in order to minimize ray aberrations to a level below the diffraction-limited beam waist size of 200 nm ðhorizontalÞ × 100 nm ðverticalÞ. After applying this methodology, we measured a beam waist size of 290 nm ðhorizontalÞ × 130 nm ðverticalÞ with 1 nm light using the Foucault knife-edge test. We also discuss the utility of using a grating-based lateral shearing interferometer with quantitative wavefront feedback for further improvement of bendable optics.

Metrology for the Advancement of X-ray Optics at the ALS

“…This work traces its origins to interferometry conducted on EUV optical elements designed as research prototypes for photolithography at 13.5-nm wavelength. Those tests pushed numerical aperture values up to 0.3-NA, [26].…”

“…One project at the ALS created a soft X-ray focusing-mirror test-bed where different alignment and wavefrontsensing approaches could be developed and compared side by side [25][26][27] (Figure 5). This work traces its origins to interferometry conducted on EUV optical elements designed as research prototypes for photolithography at 13.5-nm wavelength.…”

“…Recent examples of structures created specifically for metrology include: (a) a compound focal-plane metrology pattern used for KB mirror testing [26]; (b) pinholes for generating spherical wavefronts; and (c) binary pseudo-random (BPR) patterns [17] (described above) used to provide detailed characterizations of the resolution of optical and X-ray microscopes.…”

A Precision Grazing-incidence Angle Error Measurement of a Hard X-ray Condenser Mirror Using Single-grating Interferometry

“…Filtered through this grating, the self-image generates a Moiré fringe that is scanned to obtain the wavefront shape. In this case, the self-image of the phase grating is sufficiently magnified by divergence of the X-ray beam from the focal point and becomes directly observable by the area detector [21,27,32,33]. Therefore, because the Moiré fringe scan is not needed, shot-by-shot measurement becomes possible.…”

“…Talbot interferometry is widely used to sense X-ray wavefront shapes for characterizing optical systems [23][24][25][26][27][28][29][30][31][32][33] and for determining the index distribution of a phase obstacle [34][35][36][37][38][39] placed in the X-ray path. In this study, a phase grating is placed downstream of the focal point, and an area detector is placed at an appropriate distance from the grating to obtain the self-image of the phase grating.…”