A Self-Referenced Timing-Tool for High Repetition X-ray Free-Electron Laser Sources

This thesis explores a novel, highly versatile and self-referenced arrival-time detection scheme to measure the timing jitter between ultrashort X-ray pulses and optical laser pulses. These so-called timing-tools are used at free-electron laser facilities to enhance the temporal resolution of pump-probe experiments by measuring the temporal jitter of each optical / X-ray pulse pair. An interaction sample is used to imprint the X-ray arrival-time into a simultaneously propagating optical laser pulse. In contrast to other commonly used timing tools, the major advantage of the self-referenced detection scheme is its increased sensitivity, enabling the use of diamond as interaction sample for the first time. This is an important step towards reliable timing-tools at MHz repetition rate free electron laser facilities, where the commonly used interaction samples can not withstand the deposited heat load by the intense X-ray pulses. A detailed simulation in this thesis investigates the deposited heat load in commonly used timing-tool samples and in diamond at high repetition rate facilities, supporting the need for new diamond compatible timing-tools. The expected X-ray-induced refractive index change in diamond is simulated and used to calculate the self-referenced timingtool signal by propagating an optical pulse through the entire setup, including dispersive effects up to the third order. The novel self-referenced detection scheme was successfully tested at the European XFEL facility and the SPring-8 Angstrom Compact free electron LAser. At European XFEL, the MHz compatibility of the detection scheme, together with a diamond sample, was demonstrated. The timing jitter at European XFEL was measured with the radio frequency based synchronization (161 fs FWHM) and optical synchronization (90 fs FWHM) schemes. The self-referenced detection scheme was used to determine the X-ray-induced refractive index change in diamond (∆n=-5.7×10−5). The high versatility of the detection scheme was demonstrated by exploring the possibility of an in-situ timing-tool at the SPring-8 Angstrom Compact free electron LAser. A free-flowing flat-sheet liquid jet was used as interaction sample, replacing the sample volume for each measurement. The arrival-time measurements of the self-referenced timing-tool are correlated with the facilities own spatial encoding timing tool, and an excellent Pearson correlation of 0.98 is found in the analysis.