Multilayer Laue lenses for enhanced spatial resolution in dark-field x-ray microscopy

We introduce a crossed pair of multilayer Laue lenses (MLLs) as an objective for dark-field x-ray microscopy (DFXM). At the ID03 beamline at ESRF, two flat Mo/C/Si/C with a physical aperture of 50× 50 μm2 were operated confocally at 19.0 keV. The effective pupil was measured to be approximately 44× 43 μm2, corresponding to an effective numerical aperture of 1.58×10−3 at 19.0 keV. The 10% modulation-transfer-function crossings are 51.5(5) nm and 59.8(4) nm in the two image directions, while the angularly integrated analysis gives 55.6(3) nm—more than three times better than for a compound refractive lens (CRL) reference. The dark-field contrast is consistent with the bright-field response. At a sample-detector distance of 2.5 m, the x-ray magnification is 207. The efficiency of the MLL objective is 26.7%. We also characterize the instrumental reciprocal-space response for the three components of the diffraction vector. In normalized units, its rolling and longitudinal FWHMs are 0.0055(1) and 0.0062(1), respectively, and contain only weak secondary components. Finally, intensity and longitudinal-strain maps of a through-silicon-via structure show substantially improved spatial definition relative to CRL-based DFXM. This work expands the science domain of DFXM significantly, both for bulk and near-surface studies. The principal tradeoffs are a short working distance and broader reciprocal-space acceptance.