image: Figure | Comprehensive in-house pipeline for atomic-scale fabrication and in situ validation of Kirkpatrick–Baez (KB) nanofocusing mirrors at the National Synchrotron Light Source II (NSLS-II). a, Atomic-scale mirror fabrication employing ion beam figuring (IBF) for deterministic correction of elliptical surface profiles, followed by rhodium coating. b, Ex situ surface metrology demonstrating sub-nanometer residual height errors of 0.4 nm root-mean-square after IBF processing and coating. c, Numerical modeling of the nanoprobe at 12 keV using Synchrotron Radiation Workshop (SRW) to simulate wavefront propagation under partial coherence; the predicted focal spot size is 77 × 36 nm2 (V × H, Full Width at Half Maximum (FWHM)) for an 8×7 𝜇m2 secondary source aperture. d, In situ ptychographic characterization of the nanoprobe at the NSLS-II HXN beamline, yielding a reconstructed focal spot of 70.5 × 33.1 nm2 FWHM, in high agreement with the SRW simulation. e, X-ray fluorescence (XRF) microscopy of a Siemens star test structure, resolving the innermost features at length scales on the order of ∼ 30 nm. f, Quantitative validation of the fabrication–metrology loop, demonstrating spatial correspondence between ex situ surface residuals and in situ wavefront errors, thereby confirming atomic-scale deterministic fabrication performance.
Credit: Tianyi Wang et al.
As synchrotron light sources evolve toward the diffraction limit, the primary bottleneck in hard X-ray microscopy has shifted from source brilliance to wavefront transport and preservation. Nanometer-scale surface figure deviations manifest as irreversible phase aberrations, making the deterministic manufacturing of diffraction-limited nanofocusing optics the critical limiting factor.
In a new paper published in Light: Advanced Manufacturing, a team of scientists from the National Synchrotron Light Source II (NSLS-II) at Brookhaven National Laboratory (BNL) have established the first fully in-house, end-to-end pipeline in the United States that links atomic-scale fabrication and precision ex situ metrology to in situ X-ray beam validation.
The manufacturing pipeline begins with deterministic Ion Beam Figuring (IBF) and rhodium coating of elliptical Kirkpatrick—Baez (KB) mirrors. Guided by rigorous metrology combining stitching interferometry and nano-accuracy surface profiling, the team drove residual height errors down to approximately 0.4 nm root-mean-square. Utilizing these precise surface maps, they employed partially coherent wave-optics simulations to predict a focal spot of 77 by 36 nanometers. This forward prediction was rigorously validated in situ at the beamline using ptychography, which reconstructed a highly consistent 70.5 by 33.1 nanometer focal spot. To provide an independent, application-level benchmark, X-ray fluorescence imaging of a Siemens star test pattern successfully resolved features down to 30 nanometers.
To prove the pipeline's closed-loop consistency, the team numerically back-propagated the complex probe from the focal plane to the mirror pupils, demonstrating that the derived at-wavefront surface errors quantitatively mirrored the ex situ metrology residuals. The researchers summarize the significance of closing this loop:
“Ultimately, atomic-scale fabrication is necessary but not sufficient. The system-level bottleneck is the ability to carry a measured surface state through realistic wave-optics transport and recover it again from at-wavefront measurements in the real application configuration. By establishing this pipeline, we have created an integrated manufacturing framework that enables the deterministic delivery of atomic-scale optics for next-generation light sources.”
Journal
Light: Advanced Manufacturing
Article Title
In-house pipeline from atomic-scale fabrication to at-wavefront validation of synchrotron X-ray nanofocusing mirrors