X-ray optics for 50 - 100 keV undulator radiation using crystals and refractive lenses

Abstract

Compound refractive lenses (CRLs) are effective for collimating or focusing high-energy x-ray beams (50 - 100 keV) and can be used in conjunction with crystal optics in a variety of configurations, as demonstrated at the 1-ID undulator beamline of the Advanced Photon Source. As a primary example, this article describes the quadrupling of the output flux when a collimating CRL, composed of cylindrical holes in aluminum, is inserted in between two successive monochromators -- a modest energy resolution premonochromator followed by a high-resolution monochromator. The premonochromator is a cryogenically cooled, divergence-preserving, bent double-Laue Si(111) crystal device delivering an energy width ΔE/E ~10-3, sufficient for most experiments. The high-resolution monochromator is a four-reflection, flat Si(111) crystal system resembling two channel-cuts in a dispersive arrangement, reducing the bandwidth to ΔE/E < 10-4, as required for some applications. Tests with 67 keV and 81 keV photon energies show that the high-resolution monochromator, having a narrow angular acceptance of a few μrad, exhibits, a four-fold throughput enhancement due to the insertion of a CRL which reduces the premonochromatized beam's vertical divergence from 29 μrad to a few μrad. The ability to focus high-energy x-rays with CRLs having long focal lengths (tens of meters) is also shown by creating a line focus of 70 - 90 μm beam height in the beamline end-station with both the modest-energy-resolution and high-energy- resolution monochromatic x-rays.