Speaker
Description
Over the past two decades, exceptional progress has been made providing coherent x-ray beams at both high-brightness synchrotron sources and x-ray free electron lasers (XFEL). The availability of these coherent x-rays has led to a surge in instruments that exploit x-ray coherence for either x-ray photon correlation spectroscopy (XPCS) or coherent diffraction imaging (CDI). A key to these techniques has been to resolve, or at least nearly resolve, the speckles associated with the scattering from structural disorder, either static or dynamic, that exists in condensed matter systems. Since the resolution of x-ray detectors, particularly at high frame rate, is limited by pixel size, the needed angular resolution has been achieved by moving the detector much farther (often 10-20 meters) from the source.
Conventionally, the momentum transfer, and hence the length scales studied, has been adjusted by changing the 2θ value of the scattered x-rays from forward scattering. This approach requires moving large detectors over significant physical distances, a process that is both slow and that uses a large amount of floor space. At both synchrotrons and XFELs, space is limited, and a much more efficient system would be achieved if we could change the direction of the incoming x-rays instead of the scattered x-rays, thus leaving the detector fixed.
We have been exploring an instrument design that can efficiently provide a long sample-detector distance while maintaining the ability to rapidly set momentum transfer by inserting crystals with different order in the incident beam, thus changing in incident direction instead of moving the detector.
We will present the results of numerical simulations of a conceptual instrument including wave front propagation of both synchrotron and XFEL beams through the instrument, analysis of speckle size and contrast for as well as the signal-to-noise ratio for several classes of samples using the optimized beam and sample parameters.
This work was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515. Work by H.L. was supported by U.S. Department of Energy, Office of Science under DOE (BES) Awards DE-SC0022222.
| I plan to submit also conference proceedings | Yes |
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