Cavity based x-ray free electron laser demonstrator at the European X-ray Free Electron Laser facility

Polarization Based Out-Coupling for Cavity Based X-ray FELs

“…It is clear that for the technique to be effective, it is important to stay very close or ideally on the Θ B = 45 • line. Nonetheless, compared to other out-coupling techniques of similar simplicity, in particular the sideband transmission initially used for the EuXFEL experiment [20] or thin drum head crystals, this downside can still be preferable to the decreased time-bandwidth product of the prior and the reduced mechanical stability of the latter method. As such, it might still be interesting for the rectangular Θ B = 45 • CBXFEL demonstrator at SLAC.…”

“…In the top row, a full angular scan over both pitch and roll is shown, while in the bottom row the angles are moved along one of the lines depicted in the top row, keeping the Bragg angle fixed to a specific value. The calculations were done for a comparably thick t c =100 µm diamond with <1 0 0> surface orientation 3 , which is the crystal of choice for the European XFEL CBXFEL experiment [20]. From the transmission plot in the top right as well as the green lines in the bottom row, we see that the out-coupling technique is very sensitive to the Bragg angle, in accordance with the dependence of the polarization factor P π on Θ B , with the transmission quickly dropping when moving away from Θ B = 45 • .…”

“…The fundamental commonality of these schemes are that they are based on trapping FEL radiation inside a X-ray optical cavity, using monochromatizing crystals based on Bragg reflection instead of total reflecting optical mirrors. Due to the promise of delivering outstanding radiation properties, CBXFELs have received growing interest in the recent years [3,4,5,6,7,8,9,10,11,12,13,14]. Currently, there are two projects to install proof-of-concepts CBXFEL experiments at the European XFEL [15] and the Linac Coherent Light Source-II (LCLS-II) [16], respectively.…”

“…Same as for optical laser cavities, a major challenge of CBXFELs is how to efficiently couple out the radiation. The options to do that range from X-ray optics based techniques (see for example [18,19,13,12]) to electron beam based ones (see for example [1,20,21,14]). In this contribution, the use of the strong polarization dependence of Bragg reflection is studied as an X-ray optics based approach for radiation out-coupling, applicable both to low-gain XFELO sources, requiring low cavity losses, as for high-gain XRAFEL sources, which can take advantage of high out-coupling rates.…”

Investigating ultrafast structural dynamics using high repetition rate x-ray FEL radiation at European XFEL

“…A corresponding project is currently started and an extension of this capability to SASE2 is possible at a small extra effort. A third project is the implementation of a prototype X-ray FEL oscillator in the SASE1 source [46]. This source would provide fully coherent and narrow-band x-ray pulses needed for non-linear and quantum optical applications, but may provide critical performance as well for high resolution x-ray spectroscopy experiments.…”