First all optical synchronization in X-ray free electron laser

At the soft X-ray free-electron laser (XFEL) facility, FLASH, in Hamburg, Germany, all-optical synchronization has finally been achieved. Scientists are reporting that the timing is better than 30 fs rms for 90 fs X-ray photon pulses. As one of the most promising experiments using XFEL is time-resolved analysis based on the pump & probe scheme, it is crucial to synchronize all independent components, including all accelerator modules and all external optical lasers, to better than the delivered free-electron laser pulse duration such as shorter than 100 fs. For more information, see the paper, "Femtosecond all-optical synchronization of an X-ray free-electron laser", S. Schulz et al., Nature Communications, 6, 5895 (2015).