Femtosecond all-optical synchronization of an X-ray free-electron laser

TLDR

X‑ray free‑electron lasers require pulse durations and time resolutions of only a few femtoseconds for advanced applications. The goal is to generate and use such femtosecond pulses by synchronizing all accelerator modules and external optical lasers to better than the pulse duration. All‑optical synchronization techniques lock all independent components simultaneously to achieve this precision. We achieved facility‑wide timing better than 30 fs r.m.s.

Abstract

Many advanced applications of X-ray free-electron lasers require pulse durations and time resolutions of only a few femtoseconds. To generate these pulses and to apply them in time-resolved experiments, synchronization techniques that can simultaneously lock all independent components, including all accelerator modules and all external optical lasers, to better than the delivered free-electron laser pulse duration, are needed. Here we achieve all-optical synchronization at the soft X-ray free-electron laser FLASH and demonstrate facility-wide timing to better than 30 fs r.m.s. for 90 fs X-ray photon pulses. Crucially, our analysis indicates that the performance of this optical synchronization is limited primarily by the free-electron laser pulse duration, and should naturally scale to the sub-10 femtosecond level with shorter X-ray pulses.