This paper presents the development of a new reflection model for describing X-ray diffraction from mosaic crystals. In contrast to the well established diffraction model of Zachariasen [Zachariasen (1994), Theory of X-ray Diffraction in Crystals. Mineola: Dover Publications], it gives additional information on the spatial reflection behaviour and not just on the depth-integrated reflectivity of the crystal material. The new reflection model enables a concrete description of mosaic crystal performance in an arbitrary X-ray spectrometer configuration. Multiple reflections inside the crystal are described by splitting the calculation into a discrete number of reflections. Hence, the influence of each number of reflections is investigated, leading to a laterally resolved solution for the reflectivity. In addition, the model can use a mosaicity of arbitrary shape. This is important because the present work uses a Lorentzian-shaped mosaicity instead of a Gaussian one, which is usually the case in the most widely used simulation programs. A comparison between the new model and that of Zachariasen is performed, and it predicts a similar integrated reflectivity with a deviation lower than 0.7%. Further, a ray-tracing simulation with multiple reflections based on the new model is compared with a measurement, showing a deviation of lower than 5%.

Highly annealed pyrolytic graphite (HAPG) is an advanced type of pyrolytic graphite that, as a mosaic crystal, combines high integral reflectivity with a very low mosaicity of typically less than 0.1°. When used as dispersive X-ray optics, a high resolving power has been observed, rendering HAPG very suitable for applications in high-resolution X-ray spectroscopy, which conventionally relies on ideal crystals. For the design and modelling of HAPG crystals in applications requiring high spectral resolution, the diffraction properties must be known very accurately. To close this gap, a comprehensive characterization of HAPG crystals was performed that allows for modelling of the diffraction properties in different diffraction orders over a broad spectral range. The crystal properties under investigation are the mosaic spread, the peak reflectivity and the intrinsic reflection width. The investigations were carried out for different thickness crystal films, which were mounted adhesively on a substrate. It is shown that the diffraction properties are strongly correlated to the grade of adhesion, which depends crucially on the substrate material and its surface properties. The investigations were performed using monochromated tunable synchrotron radiation of high spectral purity with a high-precision experimental setup and calibrated detection devices at the electron storage ring BESSY II.

This paper presents recent achievements in laboratory based instrumentation for X-ray Absorption Fine Structure Spectroscopy (XAFS). The key component of the spectrometer is a HAPG mosaic crystal, which is employed in the von Hamos geometry. Due to the high efficiency of HAPG a low power micro focus X-ray tube can serve as an X-ray source. Besides a description of the spectrometer, the paper covers the treatment of the CCD images in detail. The latter is crucial in order to entirely exploit the potential of the HAPG (Highly Annealed Pyrolitic Graphite) spectrometer. One section is dedicated to applications. As a first kind of application, the concentrations of two different iron species in mixtures are determined. A second kind of typical usage of XAFS is the determination of bond lengths from the EXAFS. This XAFS application is demonstrated with metallic Ni as a reference material.

We present a novel, highly efficient von Hamos spectrometer for X-ray emission spectroscopy (XES) in the laboratory using highly annealed pyrolitic graphite crystals as the dispersive element. The spectrometer covers an energy range from 2.5 keV to 15 keV giving access to chemical speciation and information about the electronic configuration of 3d transition metals by means of the Kβ multiplet. XES spectra of Ti compounds are presented to demonstrate the speciation capabilities of the instrument. A spectral resolving power of E/ΔE = 2000 at 8 keV was achieved. Typical acquisition times range from 10 min for bulk material to hours for thin samples below 1 μm.

Ultrafast X-ray absorption spectroscopy (UXAS) offers the opportunity to investigate function-structure relationships of complex organic molecules or biological functional subunits without the need of crystallization. Of special interest from the viewpoint of structural biology is the region of K-edges of transition metals between 5 and 10 keV. Regardless of successful application of time-resolved diffraction techniques to investigations of crystal dynamics using synchrotron and laboratory based sources there are only very few examples for application of UXAS to revealing the structural dynamics in biomolecular systems. This is mainly caused by the lack of broadband ultrafast x-ray sources as well as of appropriate optics adapted to these sources. Due to the long-data-recording time in UXAS experiments the sample integrity is mainly determined by the average power of the pump pulses inducing the structural changes. Using a fixed energy of the pump pulse the latter one is determined by the repetition rate of the pump laser. In this paper we discuss the prospects of UXAS comparing fs laser plasma sources with different repetition rates in combination with tailor-made optics based on highly annealed pyrolytic graphite (HAPG).