Fakultät IV

In the exploration of universe and matter, the treatment of inverse problems is often one of the central challenges. In many experimental investigations, which are carried out in particular at large-scale research facilities such as FRM II, DESY or European XFEL, the essential phase information in the experimental data is lost due to the measurement principle (phase problem). Therefore, methods based on direct inversion are not applicable, so that the solution of the underlying non-convex optimization problem is usually very time-consuming and expensive to implement. The stated goal of our project VIPR is to develop a flexible software framework for data-driven solution of inverse problems using invertible neural networks.The main application areas envisioned include grazing incidence small- and wide-angle scattering with both neutrons and x-rays, neutron/x-ray reflectivity, and ptychography. Development will also take into account requirements from spectroscopy and particle physics.

ErUM Materie

BMBF

2022 - 2025

Microsecond X-ray photon correlation spectroscopy at the ESRF-EBS

Universität Siegen

The European Synchrotron ESRF, Grenoble, France

The objective of this proposal is to provide instrumentation which facilitates measuring microsecond dynamics in radiation prone samples such as protein systems via multispeckle X-ray photon correlation spectroscopy (XPCS) at the ESRF-EBS. We propose to purchase and integrate an XSPA RIGKAU detector for the new coherence flagship beamline ID 18 at ESRF-EBS making ideal use of the increased coherence properties of the EBS. We will construct an in-line dynamic light scattering (DLS) setup for quantifying beam induced changes to the dynamics and an X-ray shutter system with flexible opening times which allows a multiple-tau sampling scheme adapted to the shape of correlation functions. In combination with advanced sample environments, we will provide the XPCS user community the possibility to measure dynamics of radiation sensitive samples with minimum dose. We plan to position the instrumental XPCS capabilities first at ID02 for testing, commissioning and implementation for user experiments. With the completion of ID18 we will transfer it to the new beamline

Röntgen Angström Cluster

BMBF

Swedish Research Council

2020 - 2024

Dynamics of proteins in crowded environments on multiple length and time scales

Universität Siegen

Universität Tübingen

Universität Lund

Universität Stockholm

DESY, Hamburg

European XFEL, Hamburg

MaxLab, Lund

ESRF, Grenoble

ILL, Grenoble

The scientific objective of this consortium is to explore the dynamics of proteins in crowded environments, in condensates and during phase transitions on the relevant length and time scales. Protein dynamics on time scales from 10^-7 to 10² seconds will be measured by means of X-ray photon correlation spectroscopy (XPCS) at synchrotron and XFEL (X-ray free electron laser) sources. These experiments will be complemented with neutron spectroscopy techniques such as neutron spin echo (NSE) and neutron backscattering (NBS), which will give us access to the short-time dynamics of proteins on time scales ranging from 10^-12 to 10^-7 seconds. By making use of the synergy between XPCS and neutron spectroscopy, we will explore the full temporal and spatial window of protein dynamics in dense environments.

Verbundforschung

BMBF

2019-2022

BIO - XPCS

Universität Siegen

DESY, Hamburg

European XFEL, Hamburg

The objective of this project is to construct and commission a new set-up at beamline P10, DESY which allows to investigate dynamics in biological system by means of X-ray photon correlation spectroscopy (XPCS).

Röntgen Angström Cluster

BMBF

Swedish Research Council

2013-2016

Soft matter in slow motion

Universität Siegen

Universität Götheborg

Universität Rostock

DESY, Hamburg

European XFEL, Hamburg

The objective of this project is to investigate slow dynamics in soft matter systems by means of X-ray photon correlation spectroscopy (XPCS).

DFG

Ultrafast dynamics of chiral spin structures in magnetic multilayer systems

Universität Siegen

The aim of this project is to study the ultrafast dynamics of chiral spin structures by employing time-resolved X-ray resonant magnetic scattering methods using both X-ray free-electron laser sources and sources based on higher harmonic generation in the laboratory. We propose to employ IR and X-ray excitation of different magnetic systems displaying chiral magnetic order and to probe the temporal evolution of the chiral and collinear magnetic order parameters, respectively. Since the characteristic timescale for the onset of the chiral magnetic order and its ultrafast dynamics are unexplored up to now, we need to ascertain both order parameters, as they hold fundamental insights into the underlying physical mechanisms and allow us to gauge the ultimate speed for the manipulation of chiral magnetism, e.g. for ultrafast writing of chiral spin textures. We propose to investigate the following aspects of ultrafast dynamics of chiral magnetism in multilayer systems: (i) the role of size and sign of the Dzyaloshinskii-Moriya interaction in ferromagnetic systems, (ii) the behavior of spin spirals in synthetic antiferromagnetic systems and (iii) static and dynamic properties of chiral topological objects such as skyrmions.

DFG / NFDI

DAPHNE4NFDI

Siegen

Berlin

Kiel

Tübingen

Göttingen

Wuppertal

München

Nürnberg

DESY

FZJ

FRM II

Hereon

ESRF

European XFEL

EMBL

Making research Data fair for the X-ray and neutron scattering community in Germany. Developing schemes for metadata capture and archiving, developing electronic logbooks, developing analysis software for producing processed data, developement of X-ray and neutron data repositiories. Contributing to the construction of a national data infrastructure (NFDI) in Germany in collaboration with others partner consortia such as FAIRMAT, PUNCH4NFDI, MATWERK, NFDI4CHEM, NFDI4CAT. Introducing conceptes of data management into university curricula.

DFG

Skin-depth resolved surface plasma dynamics of laser-excited dense-plasmas by grazing incidence X-ray surface scattering using X-ray free-electron laser

Universität Siegen

European XFEL, Hamburg

The interaction of high-intensity lasers with solids creates high-density, warm-to-hot temperature plasmas involving a wide range of nonlinear physics phenomena. Such plasmas are not only of great relevance to astrophysics and inertial confinement fusion, but also hold promise for the generation of bright, coherent light sources and for bright particle beams including ions. Here, efficiently depositing laser energy into plasmas is a key. In general, laser coupling into plasmas occur either in the under-critical density part of the expanding plasma-vacuum interface, where the laser wave propagates, or within the skin depth of the overcritical plasma, where the laser wave is evanescent. The so-called critical density nc is located at a position in the density profile where the local electron plasma frequency equals the laser frequency, which is about 1% of the solid density for optical frequencies. It is known that a sub-μm scale density profile at the surface strongly influences the laser-plasma coupling. To obtain a complete picture of the laser-plasma coupling and the subsequent energy transport into the bulk, it is therefore crucial to know the dynamically changing over-critical plasma profile with nanometer (or skin-depth) resolution. Our project aims at visualizing surface plasmas employing X-ray free electron lasers providing the required nm scale surface sensitivity on ultrafast time scales.

DFG

Depth-resolved distribution of ultrafast spin currents and fluctuations in magnetic structures

Universität Siegen

We propose to directly measure the ultrafast spatial evolution of laser-excited spin and charge densities inside magnetic multilayer samples employing ultrafast XUV and soft X-ray magnetic reflectivity experiments at HHG and XFEL sources. Using the coherence properties of the ultra-short FEL pulses we also aim at measuring the temporal fluctuations of spin and charge densities by means of resonant magnetic X-ray photon correlation spectroscopy. Both information, the temporal evolution of the spin and charge densities and their respective fluctuations will help to unravel the microscopic details of processes involved in ultrafast magnetization dynamics.

DFG

X-ray specular and off-specular diffuse scattering of magnetic interface structures at XFEL sources - investigating ultrafast spin transport processes

Universität Siegen

Recent experiments on fs time scales revealed unusual quenching mechanisms in magnetic multilayer systems, which hint towards a spatial component accompanying the demagnetization process. This is currently interpreted in terms of ultrafast spin-diffusion processes through magnetic materials and across interfaces yielding an ultrafast spin-dependent transport process. We want to study such magnetic interfaces using soft X-ray and XUV radiation in reflection geometry. This scattering geometry allows to map out the charge and spin density profiles of interfaces and surfaces of magnetic multilayer systems and to identify positions in reciprocal space being particular sensitive to changes in the spin-system.

Using XFELs in the XUV regime we want to measure time resolved the evolution of spin and charge profiles across interface structures upon irradiation with an ultra-short IR laser pulse. The experiments shall investigate details of the ultrafast spin diffusion processes across interface structures. Reflectivity yields details of the perpendicular density profile while the diffuse scattering channels allow to follow magnetic correlation lengths parallel to the interface in a depth resolved manner. Thus we want to map out the full available Q-space upon irradiation with an ultrashort laser pulse to follow the details of the space and time evolution of the corresponding spin profiles. The results will give unique insights into the physics of spin diffusion and transport processes across magnetic interface structures.

others

Eu-XFEL R&D Proposal

High-resolution characterization of high-intensity laser interaction with dense-plasmas using time-resolved grazing-incidence small-angle x-ray scattering (TR-GISAXS)

European XFEL

Universität Siegen

The objective of this proposal is to provide the HED instrument with a capability of in-situ high-resolution characterization of the solid-density plasma surfaces under UHI laser interactions. This has not been achieved elsewhere in the world, thus will provide a unique capability to users to perform experiments in well-characterized and well-controlled manner. In addition, our project will also benefit high-pressure community users using nanosecond laser compression (another main pillar of HED/HIBEF), as the laser-absorption, subsequent electronic heat conduction and ion heating to initiate ablation at surface is a common issue here.

Aktualisiert via XIMS am 13.3.2023 von C. Gutt