Paper

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

Diez, Michael, Schulz, Sebastian, Hartmann, Nick, Wagner, Martin S, Sato, Tokushi, Yabashi, Makina, Katayama, Tetsuo, Galler, Andreas, Heider, Rupert, Helml, Wolfram, Coffee, Ryan N, Boemer, Christina, Bressler, Christian, Sato, Takahiro

2021

Overview

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 \\(\\mu\\)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.

• Publisher: Cornell University Library, arXiv.org
• Subject: Femtosecond pulses / Free electron lasers / Time lag