Lorenz-M. Stadler

Measuring temporal speckle correlations at ultrafast x-ray sources

We present a new method to extract the intermediate scattering function from series of coherent diffraction patterns taken with 2D detectors. Our approach is based on analyzing speckle patterns in terms of photon statistics. We show that the information obtained is equivalent to the conventional technique of calculating the intensity autocorrelation function. Our approach represents a route for correlation spectroscopy on ultrafast timescales at X-ray free-electron laser sources.

Soft x-ray holographic microscopy

We present a new x-ray microscopy technique based on Fourier transform holography (FTH), where the sample is separate from the optics part of the setup. The sample can be shifted with respect to the holography optics, thus large-scale or randomly distributed objects become accessible. As this extends FTH into a true microscopy technique, we call it x-ray holographic microscopy (XHM). FTH allows nanoscale imaging without the need for nanometer-size beams. Simple Fourier transform yields an unambiguous image reconstruction. We demonstrate XHM by studying the magnetic domain evolution of a Co/Pt multilayer film as function of locally varied iron overlayer thickness.

Digital In-line Holography with femtosecond VUV radiation provided by the free-electron laser FLASH

Femtosecond vacuum ultraviolet (VUV) radiation provided by the free-electron laser FLASH was used for digital in-line holographic microscopy and applied to image particles, diatoms and critical point dried fibroblast cells. To realize the classical in-line Gabor geometry, a 1 microm pinhole was used as spatial filter to generate a divergent light cone with excellent pointing stability. At a fundamental wavelength of 8 nm test objects such as particles and diatoms were imaged at a spatial resolution of 620 nm. In order to demonstrate the applicability to biologically relevant systems, critical point dried rat embryonic fibroblast cells were for the first time imaged with free-electron laser radiation.

Diffusion Studies in Ordered Alloys

1. Introduction Diffusion is an important and fundamental phenomenon for the properties and the behavior of metals, alloys, semiconductors, ceramics, glasses and polymers at higher temperatures. It plays an important role in the kinetics of microstructural changes of a material. It is a driving force for nucleation of new phases, recrystallization and phase transformations with a wide use in current technology, e.g. surface hardening, changing of deformation behavior by nucleation, diffusion doping or sintering. Especially the intermetallic alloys attracted attention as suitable materials for high-temperature applications due to their corrosion stability and strength. Many of the physical processes, developed for intermetallics are applicable for diffusion in all crystalline solids. The knowledge of the diffusion behavior of intermetallic alloys is, therefore, of interest for basic material science and for their use in technological applications. [1]