The XUV split-and-delay unit at beamline BL2 at FLASH

Abstract

For time-resolved extreme ultraviolet (XUV) pump-XUV probe experiments at the Free electron LASer in Hamburg (FLASH), a split-and-delay unit (SDU) has been built. It is implemented in beamline BL2 which provides a focal spot size of about 20 μm diameter in the experiment. The beam is divided geometrically into two paths which can be delayed from −3 to +15 ps with respect to each other. The transmission up to 200 eV photon energy is above 35% in one beam path and 74% in the other. The latter transmits the XUV beam again from 305 to 570 eV (>1% transmission). Thus almost the whole spectral range at FLASH is covered by the SDU with reasonable transmission, including the option to transport high-energy third harmonic radiation in one of the beam paths. Both beam paths are realigned into the original direction of the radiation at the end of the SDU. Thus the utilization of the divided as well as the original beam is enabled by simply moving the optical elements of the SDU into or out of the beam. Using the SDU, the coherence length and the average pulse duration at FLASH was determined to be 0.9-1.8 μm, depending on the wavelength, and about 30 fs, respectively, for the specific electron bunch parameters.

Free-electron laser induced processes in thin molecular ice

“…33,34 This SDU provides two jitter-free replica pulses for XUV pump-XUV probe experiments (see Fig. 2a).…”

A hard x-ray split-and-delay unit for the HED instrument at the European XFEL

“…The x-ray pulses are split at a sharp edge of a wavefront beam-splitter and then propagate through two delay branches with adjustable optical path lengths. For the XUV and soft x-ray spectral regime a similar set-up with carbon coatings instead of multilayer mirrors has been integrated into the FLASH SASE FEL [3]. With this device the spatio-temporal coherence properties [4,5] as well as the pulse duration [6] of a soft x-ray FEL have successfully been measured for the first time.…”

A hard x-ray split-and-delay unit for the HED experiment at the European XFEL

“…Due to the high absorbance and the small reflectivity at large incident angles a grazing incident geometry is utilized. For the XUV-and soft x-ray spectral regime such a set-up has successfully been integrated into the FLASH SASE FEL [9]. With this device the spatio-temporal coherence properties [7,8] as well as the pulse duration [10] of a soft x-ray FEL have successfully been measured for the first time.…”

“…Further, direct measurements of the temporal coherence properties will be possible by making use of a linear autocorrelation [7,8]. The set-up is based on geometric wavefront beam splitting, which has successfully been implemented at an autocorrelator at FLASH [9]. The x-ray FEL pulses are split by a sharp edge of a silicon mirror coated with multilayers.…”