Educational Impact

1. Systematic Study of Variable Coherence in X-ray Diffraction from NanocrystalsI. K. Robinson, Physics Dept, University of IllinoisDMR-0308660 “Coherent X-ray Diffraction Imaging of Nanocrystals” We have discovered that the coherence of the powerful 3rd generation APS X-ray source can be preserved even after the introduction of condenser optics before the sample. The image on the right shows 10 frames of a movie of coherent diffraction fringes measured from a gold nanocrystal. As the movie plays, the entrance aperture enlarges steadily from 10 to 100 microns in the vertical direction, while the focal spot on the sample stays constant at 1 micron. The vertical fringe contrast is seen to diminish strongly, while in the horizontal it is virtually unchanged. The effect was predicted theoretically by the calculation shown below of the Fourier transform of a simple object (left) with the addition of a parabolic phase function (right), that represents illumination by a spherical wave instead of a plane wave.

2. Educational Impact The experiment was carried out by Meng Liang, a new graduate student training in the area of CXD. She plans to analyze these new data for publication. The previous students have started postdoc positions where the are passing on their knowledge of coherent diffraction to other groups. Broader Impact Coherence at X-ray wavelengths is a rather abstract quantity, understood in theory, but, until now, not easily related to experiments. The results of these experiments should have a strong impact on the design of future experiments at both synchrotron X-ray sources and future free-electron lasers, such as SLAC’s LCLS. Systematic Study of Variable Coherence in X-ray Diffraction from NanocrystalsI. K. Robinson, Physics Dept, University of IllinoisDMR-0308660 “Coherent X-ray Diffraction Imaging of Nanocrystals”