Optimizing XFEL experiment methodology through start-to-end simulations

• Juncheng E (Eur.XFEL (European XFEL))

The development of X-ray Free-Electron Lasers (XFELs) has provided unprecedentedly bright X-rays. These high intensity X-rays with ultra-short pulses provide an opportunity to explore the structure and dynamics of matter in ever more fine spatial and temporal resolutions. However, to best exploit these new machines is nontrivial: researchers need to adapt various methodologies to XFEL experiments and optimize the experimental parameters for the best data quality within a limited experimental time. In order to find the optimal methodology and parameters for any given experiment, we present a start-to-end simulation workflow that incorporates various simulation modules: including the XFEL SASE source, X-ray wave propagation, photon-matter interaction and scattering signal generation. With this thorough simulation tool, we use the example of single particle imaging of biological molecules in a variety of experimental conditions to explore the value of such simulations and draw first conclusions about an optimal experiment within the parameters explored.

Self-Amplification of Coherent Energy Modulation in Seeded Free-Electron Lasers

• Jiawei Yan (SARI Shanghai)

Seeded free-electron lasers (FELs) are ideal for providing fully coherent soft X-ray pulses. However, it is challenging to operate seeded FELs at a high repetition rate due to the limitations of present state-of-the-art laser systems. In this talk, we report a novel self-modulation method for enhancing laser-induced energy modulation, thereby relaxing the peak power requirement of an external seed laser by more than an order of magnitude. Driven by this scheme, we experimentally realize high harmonic generation in a seeded FEL using an unprecedentedly small external laser-induced energy modulation at the Shanghai soft X-ray FEL. An electron beam with a laser-induced energy modulation as small as 1.8 times the slice energy spread is used for lasing at the 7th harmonic of a 266-nm seed laser in a single-stage high-gain harmonic generation (HGHG) setup and the 30th harmonic of the seed laser in a two-stage HGHG setup. The results mark a significant step towards a high-repetition-rate, fully coherent X-ray FEL.