arXiv subjects

Kai Bagschik

Publications and source records attributed to Kai Bagschik.

5 recordsLinked to original sources

arXiv2025

Picosecond localization dynamics following ultrafast nanoscale magnetic switching

Ultrashort laser pulses provide the fastest known way to switch magnetic order. Such excitation commonly creates nanometer-scale domains, even after homogeneous illumination when the position of nucleated domains is not externally defined. However, the physics of domain localization during such ultrafast phase transitions remains unresolved. Here, we use shot-resolved pump-probe resonant x-ray scattering together with a material featuring a periodically modulated magnetic anisotropy landscape to track, in real time, the laser-driven nucleation and localization of nanometer-scale spin textures. We find that nucleation and localization are two distinct processes. Nucleation occurs homogeneously via fluctuations at early times, whereas spatially periodic structures emerge only later and, under suitable conditions, localize in less than one nanosecond. Real-space simulations show that this localization is governed by strong lateral variations in spin-texture lifetimes. Our results demonstrate that ultrafast phase-transition dynamics fundamentally differ from conventional transitions, yet still can be controlled through moderate nanometer-scale tailoring of the energy landscape.

cond-mat.mes-hall↗

arXiv2025

Generic Rolling Access to Synchrotron Radiation Facilities

A generic model for rolling access to synchrotron radiation experiments is presented, which has the capacity to replace call-based access models. Proposal submission, evaluation and scheduling are all executed in a rolling fashion. This significantly reduces the waiting times between proposal submission and experiment execution than that of the call-based access model. The generic rolling access model is in principle applicable to any beamlines, regardless of the number of experimental methods or setups it provides to users. This access model is flexible and could provide faster access compared to call-based access model as well as accommodate experiments and projects requiring extended preparation times.

physics.acc-ph↗

arXiv2024

Spatial coherence of synchrotron radiation degraded by grating monochromators

In this work, we present a physical and theoretical description of the significant degradation of X-ray spatial coherence properties due to the use of grating monochromators at synchrotron facilities. We present a comprehensive study of the effects of spatial coherence degradation as a function of grating parameters under different focusing and propagation conditions. The focus is on the effect of spatial coherence degradation caused by the grating alone, starting from a fully coherent incident photon beam generated by a filament source. The mathematical description and theoretical analysis of the spatial coherence degradation is presented in the framework of statistical optics.

physics.optics↗

arXiv2023

Coherent x-ray magnetic imaging with 5 nm resolution

Soft x-ray microscopy plays an important role in modern spintronics. However, the achievable resolution of most x-ray magnetic imaging experiments is above 10 nm, limiting access to fundamental and technologically relevant length scales. Here, we demonstrate x-ray magnetic microscopy with 5 nm resolution by combining holography-assisted coherent diffractive imaging with heterodyne amplification of the weak magnetic signal. The gain in resolution and contrast allows direct access to key magnetic properties, including domain wall profiles and the position of pinning sites. The ability to detect and map such properties with photons opens new horizons for element-specific, time-resolved, and in-operando research on magnetic materials and beyond.

cond-mat.mtrl-sci↗

arXiv2020

Kinematically complete experimental study of Compton scattering at helium atoms near the ionization threshold

Compton scattering is one of the fundamental interaction processes of light with matter. Already upon its discovery [1] it was described as a billiard-type collision of a photon kicking a quasi-free electron. With decreasing photon energy, the maximum possible momentum transfer becomes so small that the corresponding energy falls below the binding energy of the electron. Then ionization by Compton scattering becomes an intriguing quantum phenomenon. Here we report a kinematically complete experiment on Compton scattering at helium atoms below that threshold. We determine the momentum correlations of the electron, the recoiling ion, and the scattered photon in a coincidence experiment finding that electrons are not only emitted in the direction of the momentum transfer, but that there is a second peak of ejection to the backward direction. This finding links Compton scattering to processes as ionization by ultrashort optical pulses [2], electron impact ionization [3,4], ion impact ionization [5,6], and neutron scattering [7] where similar momentum patterns occur.

physics.atom-ph↗