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A split-and-delay unit for the XUV and soft X-ray spectral range has been installed at beamlines FL23 and FL24 at the FLASH2 Free-Electron Laser at DESY. It enables time-resolved pump-probe experiments covering the whole spectral range of FLASH2 from 30 eV up to 1500 eV. Using wavefront beam splitting and grazing incidence mirrors a sub-fs resolution with a relative pulse delay of -5 ps ≤ uτ ≤ +18 ps is achieved. Two different mirror coatings are required to cover the complete spectral range and thus, a design that is based on a three dimensional beam path was developed. This allows the choice between different sets of mirrors with either coating for the fixed branch. In the variable branch two coatings are available on the same set of mirrors. A Ni coating allows a total transmission above T > 0.50 for photon energies between hν ≈ 30 eV and 650 eV at a grazing angle of a ϑvariable = 1.8° in the beam path with variable delay. With a Pt coating a transmission of T > 13 % is possible for photon energies up to hν = 1500 eV. In the fixed beam path at a grazing angle of ϑfixed = 1.3° a transmission of T > 60 % with a Ni coating and T > 28 % with a Pt coating is possible.

An accurate transmission measurement of thin foils (usually made of elemental metals and/or semiconductors), which routinely are used as attenuators in soft x-ray beamlines, end-stations and instruments, represents a long standing problem over the wide experimentation field with photon beams, see for example [1-4]. Such foils are also frequently utilized for blocking long wavelength emission, i.e., UV-Vis-IR radiation, from plasma and high order harmonic sources, whilst soft x-rays emitted from the source pass through the foil with only a slight attenuation. Despite the enormous amount of data available in the literature, e.g., Henke’s tables [5], measurements made on real foils often provide surprising results. In this study, a procedure based on the ablation imprints method is utilized for determination of soft x-ray filter transmission, namely the f-scan technique [6,7]. This technique combines the GMD (Gas Monitor Detector) pulse energy measurement and attenuation of the beam by foils (made of different metallic/semiconducting elements of varying thickness) with areas of ablation imprints created on a suitable target, e.g. PMMA – Poly(methyl methacrylate). The results show only a partial overlap with transmission values found in Henke’s tables. Nevertheless, a good agreement with transmission values determined by conventional radiometry techniques at synchrotron radiation beamlines has been found. Such a difference between the experimentally obtained values and transmissions calculated for a pure element is usually explained by spontaneous formation of oxidized layers on the filter surface and in the near-surface layer and their possible alteration by intense FEL radiation. The first results obtained with Al, Nb, Zr and Si filters at FLASH/FLASH2 (Free-electron LASer in Hamburg tuned to 13.5 nm) facilities will be shown and discussed in this presentation. References 1. F. R. Powell, P. W. Vedder, J. F. Lindblom, S. F. Powell: Thin film filter performance for extreme ultraviolet and x-ray applications, Opt. Eng. 29, 614 (1990). 2. E. M. Gullikson, P. Denham, S. Mrowka, J. H. Underwood: Absolute photo absorption measurements of Mg, Al, and Si in the soft x-ray region below the L2,3 edges, Phys. Rev. B 49, 16 283 (1994). 3. R. Keenan, C. L. S. Lewis, J. S. Wark, E. Wolfrum: Measurements of the XUV transmission of aluminium with a soft x-ray laser, J. Phys. B 35, L449 (2002). 4. A. Joseph, M. H. Modi, A. Singh, R. K. Gupta, G. S. Lodha: Analysis of soft x-ray/VUV transmission characteristics of Si and Al filters, AIP Conf. Ser. 1512, 498 (2013). 5. B. L. Henke, E. Gullikson, J. C. Davis: X-ray interactions: photoabsorption, scattering, transmission, and reflection at E = 50-30000 eV, Z =1-92, At. Data Nucl. Data Tables 54, 181 (1993). 6. J. Chalupsky et al.: Spot size characterization of focused non-Gaussian X-ray laser beams, Opt. Express 18, 27836 (2010). 7. J. Chalupský, T. Burian, V. Hajkova, L. Juha, T. Polcar, J. Gaudin, M. Nagasono, R. Sobierajski, M. Yabashi, J. Krzywinski: Fluence scan: an unexplored property of a laser beam, Opt. Express 21, 26363 (2013).

The physics and chemistry of liquid solutions play a central role in science, and our understanding of life on Earth. Unfortunately, key tools for interrogating aqueous systems, such as infrared and soft X-ray spectroscopy, cannot readily be applied because of strong absorption in water. Here we use gas dynamic forces to generate free-flowing, sub-micron, liquid sheets which are 2 orders of magnitude thinner than anything previously reported. Optical, infrared and X-ray spectroscopies are used to characterize the sheets, which are found to be tunable in thickness from over 1 micron down to less than 20 nanometers, which corresponds to fewer than 100 water molecules thick. At this thickness, aqueous sheets can readily transmit photons across the spectrum, leading to potentially transformative applications in infrared, X-ray, electron spectroscopies and beyond. The ultrathin sheets are stable for days in vacuum, and we demonstrate their use at free-electron laser and synchrotron light sources.

Interaction of short-wavelength free-electron laser (FEL) beams with matter is undoubtedly a subject to extensive investigation in last decade. During the interaction various exotic states of matter, such as warm dense matter, may exist for a split second. Prior to irreversible damage or ablative removal of the target material, complicated electronic processes at the atomic level occur. As energetic photons impact the target, electrons from inner atomic shells are almost instantly photo-ionized, which may, in some special cases, cause bond weakening, even breaking of the covalent bonds, subsequently result to so-called non-thermal melting. The subject of our research is ablative damage to lead tungstate (PbWO4) induced by focused short-wavelength FEL pulses at different photon energies. Post-mortem analysis of complex damage patterns using the Raman spectroscopy, atomic-force (AFM) and Nomarski (DIC) microscopy confirms an existence of non-thermal melting induced by high-energy photons in the ionic monocrystalline target. Results obtained at Linac Coherent Light Source (LCLS), Free-electron in Hamburg (FLASH), and SPring-8 Compact SASE Source (SCSS) are presented in this Paper.

A recently demonstrated single-shot measurement of the relative delay between x-ray FEL pulses and optical laser pulses has now been improved to ~10 fs rms error and has successfully been demonstrated for both soft and hard x-ray pulses. It is based on x-ray induced step-like reduction in optical transmissivity of a semiconductor membrane (Si 3 N 4 ). The transmissivity is probed by an optical continuum spanning 450 - 650 nm where spectral chirp provides a mapping of the step in spectrum to the arrival time of the x-ray pulse relative to the optical laser system.

As liver fibrosis is the result of persistent necroinflammation in the liver, pro-inflammatory cytokines secreted in response to cell injury have a central role in the pathogenesis of liver fibrosis. We aimed to investigate the association of cytokine gene polymorphism and liver fibrosis among Chinese patients with chronic hepatitis B.Polymorphisms at interleukin-10 (IL-10-627, -1117), interleukin-1-beta (IL-1beta-511, -31, -3964), interleukin-1 receptor antagonist (IL-1RN), and tumor necrosis factor-alpha (TNF-alpha-308, -238) among Chinese chronic hepatitis B patients were determined. Severe liver fibrosis was defined as Ishak fibrosis score = 4 (of 6).Fifty-nine of 273 (22%) patients had severe fibrosis. The distribution of genotypes for IL-10-627 was CC (11%), CA (41%), and AA (48%). The CC genotype at IL-10-627 was protective against severe fibrosis (odds ratio (OR) 0.11; 95% CI 0.014-0.82; P = 0.032). After adjusted for baseline variables, the adjusted OR of CC genotypes at IL-10-627 for severe fibrosis was 0.063 (95% CI 0.06-0.64; P = 0.063). Other gene polymorphisms at IL-1beta, IL-1RN, TNF-alpha, and IL-10 had no significant association with severe fibrosis. Weak linkage disequilibrium was observed between IL-10-627 and IL-10-1117 with linkage disequilibrium coefficient of 0.12 (P < 0.001). The distribution of haplotypes of IL-10-1117 and IL-10-627 was A-A (69%), A-C (26%), and G-C (5%). High and intermediate IL-10 production (A-C and G-C) haplotypes were protective against severe fibrosis (OR 0.62; 95% CI 0.39-0.99; P = 0.046).High production genotype and haplotypes of IL-10 were associated with less severe liver fibrosis in chronic hepatitis B in Chinese.

Ultra-fast soft x-ray lasers have opened a new area of laser-matter interactions which in most cases differ from the well understood interaction of UV-vis radiation with solid targets. The photon energy >30eV essentially exceeds the width of band gap in any known material and excites the electrons from the deep atomic and valence levels directly to the conduction band. Both thermal and non-thermal phenomena can occur in such a material being caused by electron thermalization and bond breaking, respectively. We report the first observation of non-thermal single-shot soft x-ray laser induced desorption oc curring below the ablation th reshold in a thin layer of poly (methyl methacrylate) - PMMA. Irradiated by the focused beam from the Free-electron LASer in Hamburg (FLASH ) at 21.7nm, the samples have been investigated by an atomic-force microscope (AFM) enabling the visualization of mild surface modifications caused by the desorption. A model describing non-thermal desorption and ablation has been developed an d used to analyze single-shot imprints in PMMA. An intermediate regime of materials removal has been found, confir ming the model predictions. We also report below-threshold multiple-shot desorption of PMMA induced by high-order harmonics (HOH) at 32nm as a proof of an efficient material remova l in the desorption regime. Keywords: soft X-ray laser, laser beam profile, ablation, desorption, poly(meth yl methacrylate) - PMMA

Single shot radiation damage of bulk silicon induced by ultrashort XUV pulses was studied. The sample was chosen because it is broadly used in XUV optics and detectors where radiation damage is a key issue. It was irradiated at FLASH facility in Hamburg, which provides intense femtosecond pulses at 32.5 nm wavelength. The permanent structural modifications of the surfaces exposed to single shots were characterized by means of phase contrast optical microscopy and atomic force microscopy. Mechanisms of different, intensity dependent stages of the surface damage are described.