THz pulse doubler at FLASH: double pulses for pump-probe experiments at X-ray FELs.
FLASH, the X-ray free-electron laser in Hamburg, Germany, employs a narrowband high-field accelerator THz source for unique THz pump X-ray probe experiments. However, the large difference in optical paths of the THz and X-ray beamlines prevents utilization of the machine's full potential (e.g. extreme pulse energies in the soft X-ray range). To solve this issue, lasing of double electron bunches, separated by 28 periods of the driving radiofrequency (at 1.3 GHz), timed for the temporal overlap of THz and X-ray pulses at the experimental station has been employed. In order to optimize conditions for a typical THz pump X-ray probe experiment, X-ray lasing of the first bunch to one-sixth of that of the second has been suppressed. Finally, synchronization of THz radiation pulses was measured to be ∼20 fs (r.m.s.), and a solution for monitoring the arrival time for achieving higher temporal resolution is presented.
['Zapolnova|Ekaterina|E|', 'Golz|Torsten|T|', 'Pan|Rui|R|', 'Klose|Karsten|K|', 'Schreiber|Siegfried|S|0000-0001-7705-649X', 'Stojanovic|Nikola|N|']
FLASH X-rays free-electron laser double electron bunches THz beamline pump–probe experiments