Long-term stable supercontinuum generation and watt-level transmission in liquid-core optical fibers

Due to their unique properties such as transparency, tunability, nonlinearity, and dispersion flexibility, liquid-core fibers represent an important approach for future coherent mid-infrared light sources. However, the damage thresholds of these fibers are largely unexplored. Here we report on the generation of soliton-based supercontinua in carbon disulfide (CS$_2$) liquid-core fibers at average power levels as high as 0.5 W operating stably for a long term (>70  h) without any kind of degradation or damage. Additionally, we also show stable high-power pulse transmission through liquid-core fibers exceeding 1 W of output average power for both CS$_2$ and tetrachloroethylene as core materials

Variable period undulator with tunable polarization

The proposed magnetic structure allows to control all the parameters of the sinusoidal magnetic field $B(s)=B_{0}·sin(2πs/λ_{U}+ϕ)$ of permanent magnet undulator: amplitude $B_0$, period length $λ_U$, and phase $ϕ$. The magnetic structure consists of diametrically magnetized cylindrical magnets at fixed positions. The field is adjusted by motorized rotation of each magnet. Tuning of radiated wavelength by changing the period length instead of field amplitude is more effective and results in a wider wavelength range and higher photon flux, especially for free electron lasers. Individual adjustment of the magnets allows for creating arbitrary shaped magnetic field and also for embedding other elements like phase shifters, dipoles, or multipole lenses into the undulator magnetic structure

Simulation framework SYRIS tested for microtomography applications at the imaging beamline P05/PETRA III

The Helmholtz-Zentrum Geesthacht, Germany, is operating the user experiments for microtomography at the beamlines P05 and P07 using synchrotron radiation produced in the storage ring PETRA III at DESY, Hamburg, Germany. In recent years the software pipeline and sample changing hardware for performing high throughput experiments were developed. To test and optimize the different measurement techniques together with quantification of the quality of different reconstruction algorithms a software framework to simulate experiments was implemented. Results from simulated microtomography experiments using the photon source characteristics of P05 will be shown

In Situ Studies of the Electrochemical Reduction of a Supported Ultrathin Single-Crystalline RuO2RuO_{2} (110) Layer in an Acidic Environment

With in situ surface X-ray diffraction (SXRD)and X-ray reflectivity (XRR) in combination with ex situcharacterization by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and cyclic voltamme-try, the electrochemical reduction of an ultrathin (1.66 nmthick) single-crystalline RuO$_2$(110) layer supported onRu (0001) is studied in an acidic environment, providingclear-cut evidence and mechanistic details for the trans-formation of RuO$_2$ to hydrous RuO$_2$ and metallic Ru. The reduction process proceeds via proton insertion into the RuO$_2$ (110)lattice. For electrode potentials (0 to−50 mV vs standard hydrogen electrode), the layer spacing of RuO2(110) increased,maintaining the octahedral coordination of Ru (SXRD). Continuous proton insertion at−100 to−150 mV leads to thetransformation of the lattice oxygen of RuO$_2$ to OH and water, which destroys the connectivity among the Ru-O6octahedronsand eventually leads to the loss of crystallinity (SXRD) in the RuO$_2$ (110)film at−200 mV accompanied by a swelling of thelayer with a well-defined thickness (XRR). During the protonation process, soluble Ru complexes may form. With XPS thetransformation of RuO$_2$ (110) to a hydrous RuO$_2$ layer is followed, a process that proceedsfirst homogeneously and at highercathodic potentials heterogeneously by re-deposition of previously electrochemically dissolved Ru complexes

The new dedicated HAXPES beamline P22 at PETRAIII

A new undulator beamline (P22) for hard X-ray photoelectron spectroscopy (HAXPES) was built at PETRA III (DESY, Hamburg) to meet the increasing demand for HAXPES-based techniques. It provides four special instruments for high-resolution studies of the electronic and chemical structure of functional nano-materials and catalytic interfaces, with a focus on measurements under operando and/or ambient conditions: (i) a versatile solid-state spectroscopy setup with optional wide-angle lens and in-situ electrical characterization, (ii) a HAXPEEM instrument for sub-µm spectro-microscopy applications, (iii) an ambient pressure system (> 1 bar) for operando studies of catalytic reactions and (iv) a time-of-flight spectrometer as a full-field k-microscope for measurements of the 4D spectral function ρ(EB,k). The X-ray optics were designed to deliver high brightness photon flux within the HAXPES energy range 2.4 – 15 keV. An LN$_2$-cooled double-crystal monochromator with interchangeable pairs of Si(111) and (311) crystals is optionally combined with a double channel-cut post-monochromator to generate X-rays with variable energy bandpass adapted to the needs of the experiment. Additionally, the beam polarization can be varied using a diamond phase plate integrated into the beamline. Adaptive beam focusing is realized by Be compound refractive lenses and/or horizontally deflecting mirrors down to a spot size of ∼20x17 µm$^2$ with a flux of up to 1.1x10$^{13}$ ph/s (for Si(111) at 6 keV)

Progress report on the XUV online diagnostic unit for the highly accurate determination of SR properties

Recent results from simultaneous long-term stability measurements of the beam position and photon energy of the synchrotron beam at the soft X-ray beamline P04 at PETRA III (DESY, Hamburg) are presented. The data was obtained by operating the built-in, non-invasive diagnostic unit directly upstream the beamline focus in parallel with a user experiment. We demonstrate that a sophisticated data evaluation based on principal component analysis results a high positional accuracy better than a few micron and a stable photon energy measurement with an uncertainty in the low ppm regime. Even subtle effects caused by abnormalities in the electron storage ring operation (e.g. short interruptions of the electron injection) are revealed hereby. Utilizing online diagnostic data for feedback controls will enable unprecedented stability of beamline operation at synchrotrons and FEL sources in the future

Diffusion of 5p-holes in BaF2\mathrm{BaF_2} nanoparticles

The kinetic parameters of core-valence luminescence for BaF$_2$ nanoparticles with different sizes were studied under synchrotron radiation excitation with photon energy of 18.8 eV at room temperature. In contrast to BaF$_2$ single crystals the decay kinetics of nanoparticles is shown to be non-exponential indicating the luminescence quenching. We assume that the quenching of core-valence luminescence is caused by the diffusion of core holes to nanoparticle surface. The diffusion length of the core holes in BaF$_2$ has been estimated as 2–3 nm using diffusion model of luminescence quenching in nanoparticles

MicroX-ray absorption near edge structure tomography reveals cell-specific changes of Zn ligands in leaves of turnip yellow mosaic virus infected plants

As many metals are essential for plants, excess or deficiency of them or alteration of their uptake, translocation, sequestration or physiological use can have severe consequences for plant growth and fitness. Therefore, investigating the distribution and speciation of metals in tissues is essential to understand plant physiology. We present a method based on non-destructive Synchrotron X-ray microtomography combined with microspectroscopy for studying metal distribution and speciation in plant tissues. By using the Maia detector system and the high flux of the undulator beam at the P06 beamline of the PETRA III synchrotron (at DESY), it was possible to record micro X-ray Absorption Near Edge Structure (μXANES) for every voxel of a tomogram. The metal coordination in regions of interest within the tissue samples could be determined by comparing the XANES with spectra of relevant reference compounds. Metal distribution and coordination were measured in shock frozen hydrated plant leaves in a cryostream, avoiding sample preparation artefacts like liquid cell content redistribution that occurs with other preparation methods, unequal distribution of stains in staining assays, sample degradation by beam damage and thawing, etc. A spatial resolution of 5 μm was selected, which is sufficient to resolve all leaf tissues (epidermis, palisade mesophyll, spongy mesophyll, veins), larger cells and biomineralization hotspots.As an application example, we studied the effect of infection with Turnip Yellow Mosaic Virus (TYMV) on the Zn distribution and the Zn speciation in duplicates of Noccaea ochroleucum. This non-accumulator plant grown with 100 μM Zn had enough metal to allow collecting significant spectroscopic data. We found that the TYMV infected samples formed biomineralization crystallites, showing strong spectroscopic similarity to Zn silicate

Secondary neutrino and gamma-ray fluxes from SimProp and CRPropa

The interactions of ultra-high energy cosmic rays (UHECRs) with background photons in extragalactic space generate high-energy neutrinos and photons. Simulating UHECR propagation requires assumptions about physical quantities such as the spectrum of the extragalactic background light (EBL) and photodisintegration cross sections. These assumptions, as well as the approximations used in the codes, may influence the computed predictions both of cosmic-ray spectra and composition, and of cosmogenic neutrino and photon fluxes. Following up on our previous work where we studied the resulting uncertainties on cosmic-ray simulations, here we quantify those on neutrinos and photons, using the Monte Carlo codes CRPropa and SimProp in various source scenarios. We discuss the results in the light of the constraining power of the neutrino and photon spectra on the origin of the UHECRs. We show that cosmogenic neutrino fluxes are more sensitive to the parametrization of the EBL than UHECR spectra, whereas the overall cosmogenic gamma-ray production rates are relatively independent on details of the propagation. We also find large differences between neutrino fluxes predicted by the latest released versions of CRPropa and SimProp, and discuss their causes and possible improvements in future versions of the codes

Emerging chromo-natural inflation

The shift-symmetric coupling of a pseudo-scalar particle driving inflation to gauge fields provides a unique way of probing cosmic inflation. We show for an SU(2) gauge group how a classical isotropic background gauge field develops from the standard quantum mechanical vacuum in the far past. Over the course of inflation, the theory dynamically evolves from an approximately abelian regime into an inherently non-abelian regime, with distinct predictions for the scalar and tensor power spectra. The latter regime closely resembles a setup known as chromo-natural inflation, although our main focus here is on a new part of the parameter space which has received little attention so far. For single-field slow roll inflation models, large scales may exit the horizon in the abelian regime, ensuring agreement with the observations of the anisotropies in the cosmic microwave background, whereas smaller scales experience the non-abelian effects. This results in a strong enhancement of the stochastic gravitational wave background at small scales, e.g. at frequencies accessible with ground-based interferometers. For the scalar power spectrum, a similar enhancement arises due to non-linear contributions