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The SASE3 soft X-ray beamline at the European XFEL has been designed and built to provide experiments with a pink or monochromatic beam in the photon energy range 250-3000 eV. Here, the focus is monochromatic operation of the SASE3 beamline, and the design and performance of the SASE3 grating monochromator are reported. The unique capability of a free-electron laser source to produce short femtosecond pulses of a high degree of coherence challenges the monochromator design by demanding control of both photon energy and temporal resolution. The aim to transport close to transform-limited pulses poses very high demands on the optics quality, in particular on the grating. The current realization of the SASE3 monochromator is discussed in comparison with optimal design performance. At present, the monochromator operates with two gratings: the low-resolution grating is optimized for timeresolved experiments and allows for moderate resolving power of about 2000-5000 along with pulse stretching of a few to a few tens of femtoseconds RMS, and the high-resolution grating reaches a resolving power of 10 000 at the cost of larger pulse stretching. [ABSTRACT FROM AUTHOR]

SASE1 is the first beamline of the European XFEL that became operational in 2017. It consists of the SASE1 undulator system, the beam transport system, and the two scientific experiment stations: Single Particles, Clusters, and Biomolecules and Serial Femtosecond Crystallography (SPB/SFX), and Femtosecond X‐ray Experiments (FXE). The beam transport system comprises mirrors to offset and guide the beam to the instruments and a set of X‐ray optical components to align, manipulate and diagnose the beam. The SASE1 beam transport system is described here in its initial configuration, and results and experiences from the first year of user operation are reported. [ABSTRACT FROM AUTHOR]

A new phenomenon on X-ray optics surfaces has been observed: the growth of nano-dots (40-55 nm diameter, 8-13 nm height, 9.4 dots µm−2 surface density) on the grazing-incidence mirror surface under irradiation by the free-electron laser (FEL) FLASH (5-45 nm wavelength, 3° grazing-incidence angle). With a model calculation it is shown that these nano-dots may occur during the growth of a contamination layer due to polymerization of incoming hydrocarbon molecules. The crucial factors responsible for the growth of nano-dots in the model are the incident peak intensity and the reflection angle of the beam. A reduction of the peak intensity ( e.g. replacement of the FEL beam by synchrotron radiation) as well as a decrease of the incident angle by just 1° (from 3° to 2°) may result in the total disappearance of the nano-dots. The model calculations are compared with surface analysis of two FLASH mirrors. [ABSTRACT FROM AUTHOR]

An amendment to this paper has been published and can be accessed via a link at the top of the paper. [ABSTRACT FROM AUTHOR]

Abstract: Zone plates are high quality optics that have the potential to provide diffraction-limited nano-focusing of hard X-ray free electron laser radiation. The present publication investigates theoretically the temperature behavior of metal zone plates on a diamond substrate irradiated by 0.1nm X-rays from the European X-ray Free Electron Laser. The heat transfer in the optic is simulated by solving the transient heat equation with the finite element method. Two different zone plate designs are considered, one small zone plate placed in the direct beam and one larger zone plate after the monochromator. The main result is that for all investigated cases the maximum temperature in the metal zone plate layer is at least a factor 2 below the melting point of the respective material, proving the efficiency of the proposed cooling scheme. However, zone plates in the direct beam experience large and rapid temperature fluctuations of several hundred Kelvin that might prove fatal to the optic. The situation is different for optics behind the monochromator with fluctuations in the 20K range and maximum temperatures well below room temperature. The simulation results give valuable indications on the temperature behavior to be expected and are a basis for future experimental heat transfer and mechanical stability investigations of fabricated nanostructures. [ABSTRACT FROM AUTHOR]

We studied experimentally and theoretically the structural transition of diamond under an irradiation with an intense femtosecond extreme ultraviolet laser (XUV) pulse of 24-275 eV photon energy provided by free-electron lasers. Experimental results obtained show that the irradiated diamond undergoes a solid-to-solid phase transition to graphite, and not to an amorphous state. Our theoretical findings suggest that the nature of this transition is nonthermal, stimulated by a change of the interatomic potential triggered by the excitation of valence electrons. Ultrashort laser pulse duration enables to identify the subsequent steps of this process: electron excitation, band gap collapse, and the following atomic motion. A good agreement between the experimentally measured and theoretically calculated damage thresholds for the XUV range supports our conclusions. [ABSTRACT FROM AUTHOR]

All carbon materials, e.g., amorphous carbon (a-C) coatings and C60 fullerene thin films, play an important role in short-wavelength free-electron laser (FEL) research motivated by FEL optics development and prospective nanotechnology applications. Responses of a-C and C60 layers to the extreme ultraviolet (SPring-8 Compact SASE Source in Japan) and soft x-ray (free-electron laser in Hamburg) free-electron laser radiation are investigated by Raman spectroscopy, differential interference contrast, and atomic force microscopy. A remarkable difference in the behavior of covalent (a-C) and molecular (C60) carbonaceous solids is demonstrated under these irradiation conditions. Low thresholds for ablation of a fullerene crystal (estimated to be around 0.15 eV/atom for C60 vs 0.9 eV/atom for a-C in terms of the absorbed dose) are caused by a low cohesive energy of fullerene crystals. An efficient mechanism of the removal of intact C60 molecules from the irradiated crystal due to Coulomb repulsion of fullerene-cage cation radicals formed by the ionizing radiation is revealed by a detailed modeling. [ABSTRACT FROM AUTHOR]