Abstract
The longitudinal coherence function at the Advanced Photon Source beamline 34-ID-C has been measured by a novel method and the coherence length (xi(L)) determined to be, xi(L) = 0.66 +/- 0.02 microm. Three dimensional Coherent X-ray Diffraction (CXD) patterns were measured for multiple Bragg reflections from two Zinc Oxide (ZnO) nanorods with differing aspect ratios. The visibility of fringes corresponding to the 002 crystal direction for each reflection were found to be different and used to map the coherence function of the incident radiation. Partial coherence was found to be associated with amplitude 'hot' spots in three dimensional reconstructions of the crystal structure.
Highlights
The mutual coherence of an electromagnetic wave is defined as the two-point correlation function of its electric field
Interferometric measurements can be difficult to achieve for hard Xrays because of the small length scales involved, yet knowledge of the coherence properties is vital for some of the newest imaging techniques being explored at third-generation sources of Synchrotron Radiation (SR)
An individual Zinc Oxide (ZnO) rod was placed in a marked corner quadrant as close to the centre as possible using a micromanipulator; Van der Waals forces attract a chosen nanorod to the manipulation probe, contact with the surface being sufficient to deposit the rod on a Si wafer substrate in a marked location
Summary
The mutual coherence of an electromagnetic wave is defined as the two-point correlation function of its electric field. We report that the visibility of the diffraction fringes due to interference between the ends of an extended object carries the same information about the coherence of the illuminating wavefield as the classical double-slit interferometer. This neatly overcomes the practical problem of cutting out two sample points in a wave field separated by a distance of the order of a micron. Advances in experimental design allowed us to measure the same fringe system for multiple Bragg peaks from the same micron-sized crystal In this way the full longitudinal coherence function has been mapped out using just two crystals
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