Timing (a) FLASH

Many fundamental processes in nature like chemical reactions or phase transitions occur on the few femtosecond time and few nanometres to few angstroms length scale. On a way to their understanding, great hope lies on investigations of their dynamic using the bright, coherent X-ray pulses from free electron lasers (FELs) that have a duration and wavelength commensurate with that of these processes.
We developed a method to measure the arrival time of the X-ray pulses at FLASH with respect to the pump-probe laser in the experimental hall on a few femtosecond timescale, making use of the THz beamline [1]. Method is easily transferable to other advanced light source working with ultrashort electron bunches and therefore of high general interest.