The ability to split femtosecond free electron laser pulses and recombine them with a precisely adjustable delay has numerous scientific applications such as X-ray Photon Correlation Spectroscopy and X-ray pump X-ray probe measurements. A wavefront-splitting based hard X-ray split-delay system is currently under development at the Linac Coherent Light Source. The design configuration uses a series of Si(220) crystal reflections in the horizontal scattering geometry. It covers an energy range between 6.5 and 13 keV, a delay range from -30 ps up to 500 ps at 8 keV. The design features two planar air bearing based linear stage delay lines for improved stability and accuracy during the delay adjustments in order to maintain spatial overlap of the two branches during a delay scan. We present the basic design concept, tolerance analysis, and estimated performance of the system.
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.