  Ultrafast x-ray photon correlation spectroscopy has been considered a
potential unique and powerful application of x-ray free electron lasers to
probe nanoscale fluctuations in disordered matter such as materials near the
glass transition or supercooled molecular liquids. XPCS in the picosecond time
scale can be realized via the split-pulse visibility spectroscopy mode using
pulse pairs generated by x-ray split delay optics. In order to satisfy the
stringent stability and mutual coherence requirement on the pulse pair
production, an amplitude-split delay line based on transmission grating beam
splitters and channel-cut crystal optics was constructed and tested at the
Linac Coherent Light Source. We report the performance of this prototype device
in the context of ultrafast XPCS and speckle visibility spectroscopy.
