Measurement of hard X-ray coherence in the presence of a rotating random-phase-screen diffuser

• Published in: Optics communications 2010-01, Vol.283 (2), p.216-225
• Main Authors: Morgan, Kaye S., Irvine, Sarah C., Suzuki, Yoshio, Uesugi, Kentaro, Takeuchi, Akihisa, Paganin, David M., Siu, Karen K.W.
• Format: Article
• Language: English
• Subjects: Beams (radiation); Bio-medical phase contrast imaging; Biological and medical sciences; Coherence; Diffusers; Electromagnetism; electron and ion optics; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; Fundamental areas of phenomenology (including applications); General aspects, investigation technics, apparatus; Imaging; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Interferometers; Optics; Physics; Prism interferometer; Rotating; Spinning; Synchrotron hard X-rays; Synchrotron radiation instrumentation; Tissues, organs and organisms biophysics; Wave optics; X- and γ-ray instruments and techniques; X-ray beams and x-ray optics; X-rays
• ISSN: 0030-4018; 1873-0310
• DOI: 10.1016/j.optcom.2009.09.023

A suitably large coherence area is important in coherent X-ray optics, when using techniques such as interferometry or phase contrast imaging (PCI). The work done by Suzuki using a prism interferometer to measure X-ray coherence at 12.4 keV [1] is here extended to consider the use of a diffuser at the bio-medical imaging energy of 25 keV. In order to achieve a broader, more even X-ray field and eliminate speckle, a spinning piece of paper may be used as a rotating random-phase screen to diffuse the hard X-ray beam, but this will concomitantly decrease the magnitude of the complex degree of second-order coherence. We also study the effect of source size and source-to-sample distance on coherence, where imaging area and required flux must be considered. Coherence measurements at the 20XU beamline at the SPring-8 synchrotron are compared to results from wave-optical computer modelling. These show that while the diffuser will decrease the magnitude of the complex degree of coherence, further free-space propagation will lessen this effect. In the design of an experiment, the collimating slit size and use of a diffuser must therefore be balanced with distance from the source, in order to maximise coherence while maintaining the desired field of view and exposure time.