Seminars Archive

THz Doubler at FLASH: a new concept for THz-XUV pump-probe experiments

Abstract
FLASH employs a unique narrowband high-field tunable THz undulator, located behind the main undulator section. Since XUV and THz pulses are produced by the same electron bunch, both pulses are synchronized down to 5 fs. However, one of the challenges, which THz-XUV pump-probe experiments face, is a big difference of the optical path between XUV and THz, due to additional collimation optics for THz. The optical difference between the pulses at FLASH is approximately 7m (21.5ns). By now this delay is compensated by specially designed narrowband XUV refocusing mirrors. Although user groups at FLASH have successfully used this method during past years, there are still some major drawbacks of this scheme, which limits the full potential of FLASH. To solve this issue, a new “THz Doubler” concept with specially tuned double electron bunches, separated by 21.5 ns has been employed at FLASH. In this case XUV and THz pulses are temporally overlapped at the experiment without the need for the XUV mirror. We have been intensely working on the characterization and optimization of the THz Doubler scheme and preparing it for the user’s experiments. In this presentation we would like to share with you the latest achievements: measurements of the jitter between the double pulses; tuning results and future perspective for implementing the scheme at FLASH.