We have evaluated the applicability of vertically-focusing kinoform lenses for tailoring the vertical coherence
length of storage-ring undulator x-ray beams so that the entirety of the coherent flux can be used for small
angle multi-speckle x-ray photon correlation spectroscopy (XPCS) experiments. We find that the focused beam
produced by a kinoform lens preserves the coherence of the incident unfocused beam and that at an appropriate
distance downstream of the focus, the diverging beam produces speckles nearly identical to those produced by
an equivalently-sized unfocused beam. We have also investigated the effect of imperfect beamline optics on the
observed coherence properties of the beam. Via phase contrast imaging and beam-divergence measurements,
we find that a horizontally-deflecting mirror in our beamline precludes us from seeing the true radiation source
point but instead acts as an apparent source of fixed size at the center of our insertion device straight section.
Finally, we discuss how expected near-future optimization of these optics will greatly benefit XPCS measurements
performed at beamline 8-ID-I at the Advanced Photon Source.
A novel ultra-high-vacuum (UHV)-compatible x-ray monochromator has been designed and commissioned at the
undulator beamline 8-ID-I at the Advanced Photon Source (APS) for x-ray photon correlation spectroscopy
applications. To meet the challenging stability and x-ray optical requirements, the monochromator integrates two new
precision angular positioning mechanisms into its crystal optics motion control system: An overconstrained weak-link mechanism that enables the positioning of an assembly of two crystals to achieve
the same performance as a single channel-cut crystal, the so called "artificial channel-cut crystal"; A ceramic motor driven in-vacuum sine-bar mechanism for the double crystal combined pitch motion.
The mechanical design of the monochromator, as well as the test results of its positioning performance are presented in
this paper.
We present design and characterization results of a novel ultra-high-vacuum-compatible artificial channel-cut monochromator that has been installed at the undulator beamline 8-ID-I at the Advanced Photon Source. The monochromator has been designed to meet the challenging stability and optical requirements of the x-ray photon correlation spectroscopy program hosted at this beamline. In particular, the device incorporates a novel in-vacuum sine-bar drive mechanism for the combined pitch motion of the two crystals and a flexure-based high-stiffness weak-link mechanism for fine tuning the pitch and roll of the second crystal relative to the first crystal.
We have implemented in the undulator first-optics enclosure of the Massachusetts Institute of Technology-McGill University-IBM Corporation Collaborative Access Team Sector at the Advanced Photon Source an x-ray beamline and a spectrometer optimized for performing small-angle, wide- bandpass, coherent x-ray scattering experiments. We describe the novel features of this set-up. The performance of the beamline and the spectrometer has been characterized by measuring static x-ray speckle patterns form isotopically disordered aerogels. Statistical analysis of the speckle patterns has been performed from which we extract the speckle width sand contrast versus wave-vector transfer and sample thickness. The measured speckle widths and contrast are compared to direct numerical evaluations of the intensity correlation function. The calculated widths are in poor agreement with the measurements but the calculated contrast agrees well with the measured contrast.
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