The generation of two X-ray pulses with tunable nanosecond scale time separations has recently been demonstrated
at the Linac Coherent Light Source using an accelerator based technique. This approach offers the opportunity
to extend X-ray Photon Correlation Spectroscopy techniques to the yet unexplored regime of nanosecond
timescales by means of X-ray Speckle Visibility Spectroscopy. As the two pulses originate from two independent
Spontaneous Amplified Stimulated Emission processes, the beam properties fluctuate from pulse pair to pulse
pair, but as well between the individual pulses within a pair. However, two-pulse XSVS experiments require the
intensity of the individual pulses to be either identical in the ideal case, or with a accurately known intensity
ratio. We present the design and performances of a non-destructive intensity diagnostic based on measurement
of scattering from a transparent target using a high-speed photo-detector. Individual pulses within a pulse pair
with time delays as short as 0.7 ns can be resolved. Moreover, using small angle coherent scattering, we characterize
the averaged spatial overlap of the focused pulse pairs. The multi-shot average-speckle contrasts from
individual pulses and pulse pairs are compared.
Yanwen Sun, Diling Zhu, Sanghoon Song, Franz-Josef Decker, Mark Sutton, Karl Ludwig, Wojciech Roseker, Gerhard Grübel, Stephan Hruszkewycz, G. Brian Stephenson, Paul H. Fuoss, and Aymeric Robert, "Characterization of the LCLS “nanosecond two-bunch” mode for x-ray speckle visibility spectroscopy experiments," Proc. SPIE 10237, Advances in X-ray Free-Electron Lasers Instrumentation IV, 102370N (Presented at SPIE Optics + Optoelectronics: April 27, 2017; Published: 23 May 2017); https://doi.org/10.1117/12.2265454.
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