A self-referenced in-situ arrival time monitor for X-ray free-electron lasers

Abstract

We present a novel, highly versatile, and self-referenced arrival time monitor for measuring the femtosecond time delay between a hard X-ray pulse from a free-electron laser and an optical laser pulse, measured directly on the same sample used for pump-probe experiments. Two chirped and picosecond long optical supercontinuum pulses traverse the sample with a mutually fixed time delay of 970 fs, while a femtosecond X-ray pulse arrives at an instant in between both pulses. Behind the sample the supercontinuum pulses are temporally overlapped to yield near-perfect destructive interference in the absence of the X-ray pulse. Stimulation of the sample with an X-ray pulse delivers non-zero contributions at certain optical wavelengths, which serve as a measure of the relative arrival time of the X-ray pulse with an accuracy of better than 25 fs. We find an excellent agreement of our monitor with the existing timing diagnostics at the SACLA XFEL with a Pearson correlation value of 0.98. We demonstrate a high sensitivity to measure X-ray pulses with pulse energies as low as 30 $$\upmu $$ μ J. Using a free-flowing liquid jet as interaction sample ensures the full replacement of the sample volume for each X-ray/optical event, thus enabling its utility even at MHz repetition rate XFEL sources.

A sensitive high repetition rate arrival time monitor for X-ray free electron lasers

“…We have demonstrated that the Maxwell-Garnett theory of dielectric mixtures, where we assume a dielectric mixture of a diamond host material and electronic polarons, describe the observed measurement very well. With the high versatility of this self-referenced timing tool, even in-situ arrival time measurements in a unstable free-flowing liquid jet are possible 37 . This can also be used to quantify the robustness of the Maxwell-Garnett model for various materials and liquids in the near future.…”

A sensitive high repetition rate arrival time monitor for X-ray Free Electron Lasers

“…We have demonstrated that the Maxwell-Garnett theory of dielectric mixtures, where we assume a dielectric mixture of a diamond host material and electronic polarons, describe the observed measurement very well. With the high versatility of this self-referenced timing-tool, even in-situ arrival-time measurements in a unstable free-flowing liquid jet are possible 33 . This can also be used to quantify the robustness of the Maxwell-Garnett model for various materials and liquids in the near future.…”

Artificial intelligence for online characterization of ultrashort X-ray free-electron laser pulses

“…There are two main reasons for a change in the kick from shot to shot. The first is the relative timing jitter between the X-ray and the streaking pulse 24 – 26 , which is unavoidable due to the stochastic generation process of the SASE mechanism and additional fluctuations in arrival time caused by air fluctuations, thermal expansion in optomechanical components, and general synchronization errors between the two separate laser pulses. The second reason for variations of the kick is the random change of the carrier–envelope phase of the streaking laser from shot to shot.…”