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Focal aberrations of large-aperture highly oriented pyrolytic graphite (HOPG) crystals in von-Hàmos geometry are investigated by experimental and computational methods. A mosaic HOPG crystal film of 100 μm thickness diffracts 8 keV x-rays. This thickness is smaller than the absorption depth of the symmetric 004-reflection, which amounts to 257 μm. Cylindrically bent crystals with 110mm radius of curvature and up to 100 mm collection width produce a X-shaped halo around the focus. This feature vanishes when the collection aperture is reduced, but axial spectral profiles show that the resolution is not affected. X-ray topography reveals significant inhomogeneous crystallite domains of 2±1mm diameter along the entire crystal. Rocking curves shift by about ±20arcmin between domains, while their full width at half-maximum varies between 30 and 50 arcmin. These inhomogeneities are not imprinted at the focal spot, since the monochromatically reflecting area of the crystal is large compared to inhomogeneities. Ray-tracing calculations using a Monte-Carlo-based algorithm developed for mosaic crystals reproduce the X-shaped halo in the focal plane, stemming from the mosaic defocussing in the non-dispersive direction in combination with large apertures. The best achievable resolution is found by analyzing a diversity of rocking curve widths, source sizes and crystal thicknesses for 8 keV x-rays to be ΔE/E ∼ 10-4. Finally a general analytic expression for the shape of the aberration is derived. © 2012 IOP Publishing Ltd and Sissa Medialab srl.

We report on the measurement of the highest purity of polarization of X-rays to date. The measurements are performed by combining a brilliant undulator source with an X-ray polarimeter. The polarimeter is composed of a polarizer and an analyzer, each based on four reflections at channel-cut crystals with a Bragg angle very close to 45°. Experiments were performed at three different X-ray energies, using different Bragg reflections: Si(400) at 6457.0 eV, Si(444) at 11,183.8 eV, and Si(800) at 12,914.0 eV. At 6 keV a polarization purity of 1.5 × 10− 9 is achieved. This is an improvement by more than two orders of magnitude as compared to previously reported values. The polarization purity decreases slightly for shorter X-ray wavelengths. The sensitivity of the polarimeter is discussed with respect to a proposed experiment that aims at the detection of the birefringence of vacuum induced by super-strong laser fields.

K-shell spectra of targets with microstructured features irradiated by an intense femtosecond laser have been studied. Examination of Kα emission from laser irradiated Si targets coated with micron-scale polystyrene spheres indicates that the emission is enhanced by a factor of ∼3 over emission from planar solids. Sphere-coated targets also emit K-shell He-like Si radiation indicating the presence of a hot dense plasma beneath the microspheres. Furthermore, Kα from Ti foils coupled to micro-tipped reentrant pyramid and wedge shaped targets has been studied, however, no significant enhancement of the Kα yield is observed for these kinds of targets. These studies illustrate that, with correct tailoring of the target surface, field enhancements can be used to increase X-ray emission from intensely irradiated targets.

Theoretical design of a new type of the bent crystal spectrometer based on a combination of the vertical dispersion principle with diffraction of x rays from the asymmetrically cut crystal is reported. The novel instrument produces simultaneously two sets of mirror-symmetric spectra, and provides large dispersion, high spectral and 1D spatial resolution with a variable magnification. The analytic formulas describing the function of the spectrometer are complemented by its detailed quantitative analysis based on the ray tracing procedure. The method for reconstruction of the recorded spectra is described, the parameters influencing the precision of the wavelength determination are discussed. The comparison of the main predicted and experimentally observed characteristics verifies the developed theory and demonstrates the spectrometer performance. The novel instrument is particularly suitable for precise measurements of profiles and positions of the narrow-band spectral features observed in the emission of laser-generated plasmas.

A crystal spectrometer has been constructed in the Focusing Compensated Asymmetric Laue geometry covering the energy range between 30 and 120 keV. We summarize the crystal optics and show the usefulness of the instrument for spectroscopy of stationary and fast moving X-ray sources. Results are reported from several tests employing a 169 Yb gamma-ray source and the Lyman radiation of one-electron Au 78+ ions travelling at a velocity corresponding to β = v / c o ≈0.44.

This article describes an efficient method for the simultaneous measurement of the integrated reflectivity of a crystal in multiple orders of reflection at a predefined Bragg angle by using the bremsstrahlung continuum from an x-ray tube in combination with an energy-sensitive detector. The technique is demonstrated with a mica crystal for Bragg angles of 43°, 47°, and 50°. The measured integrated reflectivity for Bragg reflections up to the 24th order is compared with theoretical predictions, which are also presented in this article.

We present a new x-ray spectrometer setup based on a conically curved mica crystal in the von Hamos configuration. An x-ray sensitive charge coupled device or streak camera can be easily coupled in a perpendicular orientation to the spectrally resolved x-ray line focus. Shifting the crystal along its axis of symmetry allows one to change the dispersion and the signal flux density on the detector. A large spectral range at high resolution and adjustable signal intensity is accessible with this setup.

International audience; The experimental investigation of quantum-electrodydamic contributions to the binding energies of inner shells of highly charged heavy ions requires an accurate spectroscopy in the region of hard x-rays suitable at a limited source strength. For this purpose the focusing compensated asymmetric Laue crystal optics has been developed and a twin-spectrometer assembly has been built and commissioned at the experimental storage ring of the GSI Helmholtzzentrum Darmstadt. We characterize the crystal optics and demonstrate the usefulness of the instrumentation for accurate spectroscopy of both stationary and fast moving x-ray sources. The experimental procedures discussed here may also be applied for other spectroscopic studies where a transition from conventional germanium x-ray detectors to crystal spectrometers seems too demanding because of low source intensity.

The focusing properties of asymmetrically cut bent crystals in Bragg geometry are discussed. The conditions for optimized one- and two-dimensional polychromatic imaging of x-ray sources are proposed. In particular configurations, the schemes with asymmetrically cut crystals provide smaller aberrations and slightly higher collection efficiency than symmetrically diffracting optical elements. The analytical results are cross-checked with ray-tracing simulations, the validity of theoretical predictions is verified experimentally for one-dimensional case.

Essential parameters for the application of crystals to quantitative X-ray spectroscopy are the upper wavelength limit and the quantitative reflection properties (intrinsic resolving power, luminosity) of the crystal. Due to the large lattice constant, muscovite, a mica group mineral, can be used in the wavelength range up to about 2nm. Muscovite crystals can be bent to small radii of curvature due to their favourable cleavage and elastic properties. Characteristic reflection properties at reflections 002 – 00 24 were investigated theoretically and experimentally. The integrated reflectivity was calculated for various reflections of perfect flat as well as spherically bent muscovite crystals with curvature radii R = 100 and R = 186mm. It was measured for flat crystals in the reflections 00 10 – 00 26 using CuKα- and MoKα-radiation from X-ray tubes and compared with calculations for both perfect and mosaic crystals. Available high-quality muscovite crystals have a mosaic structure with a mosaic spread of about 1 arcmin. This mosaic spread limits the spectral resolving power for high reflection orders.

Theoretical and experimental methods for the characterization of the reflection properties of flat and bent crystals are presented. The computer code DIXI for the simulation of reflection curves in the Bragg case is briefly described.Essential effects of the dynamical theory of x-ray diffraction are illustrated with selected examples. Results from diffractometric and topographic methods for quality control of bent crystals are presented.

Anisotropic elasticity corrections are taken into account to evaluate the reflection efficiency I int and the X-ray standing-wave patterns (XSWP) P(Δθ,Φ) for bent crystals, where Δθ is the angular coordinate associated with the conventional rocking curve and the phase Φ=hr p is related to the position with respect to the crystalline lattice of the adsorbed atoms on the crystal surface, contributing to the XSWP. Analytical expressions are derived for the uniform strain-gradient parameter B=1/4(∂ 2 /∂ s0 ∂ sh ) [hu(r)] governing the peculiarities of the Bragg diffraction within elastically bent crystals, where h is the reflecting vector, u(r) is the displacement vector and s 0 and s h are the dimensionless coordinates along the incident and diffracted waves, respectively. The cases of the so-called free and forced bending in the Johann and von Hamos geometries are considered. The results of the anisotropic elasticity corrections depending on the crystal-surface orientation are presented for bent silicon (111) and quartz (10.0) and (10.1) orientations.

International audience; A twin crystal-spectrometer assembly, operated in the focusing compensated asymmetric Laue geometry has been developed for accurate spectroscopy of fast highly charged heavy ions in the hard-X-ray region. Coupled to the focusing crystal optics is a specially developed two-dimensional position-sensitive X-ray detector which is necessary for retaining spectral resolution also for fast moving sources. We summarize the crystal optics and demonstrate the usefulness of the instrument for spectroscopy of both stationary and fast moving X-ray sources. Results are reported from several tests employing a 169Yb gamma-ray source and the Lyman radiation of one-electron Pb81+ ions traveling at a velocity corresponding to [beta]†[reverse not equivalent]†v/c†[approximate]†0.59. The features of the instrument presented may be useful in many applications where it appears difficult to make the leap from conventional X-ray energy measurements to wavelength-dispersive spectroscopy based on crystal optics.

Three methods (Lang-topgraphy, one-crystal-rocking curves with scan-step-registration, two-crystal-diffractometry (TCD) with a large registered area) were tested. The reached parameters as well as advantages and disadvantages are discussed. The purpose of the examination is the application of CaF2-crystals with high diameters (⪆ 100 mm) in high-performance optics for the UV-lithography. Especially in this context the influence of defects of the crystal structure on the index of refraction has been examined. Es wurden drei Methoden (Lang-Topographie, Einkristall-Rockingkurvenaufnahmen im Scan-Step-Betrieb, Zwei-Kristall-Diffraktometrie mit grosem Prufgebiet) getestet. Die erreichten Parameter sowie die Vor- und Nachteile wurden diskutiert. Hintergrund der Untersuchungen ist der Einsatz von CaF2-Kristallen groser Durchmesser (⪆ 100 mm) in optischen Hochleistungssystemen fur die UV-Lithographie und in diesem Zusammenhang der Einflus von Storungen der Kristallstruktur auf die Brechzahl.

Crystallographic and dispersion characteristics of mica at high (V—XI) reflection orders were investigated for the first time. Even the order-XI integral reflection was sufficiently strong to be used in experiments. High-precision bending of a mica crystal along a spherical surface with a small radius R = 100 mm and the use of such crystal analysers in focusing spectrographs with one-dimensional and two-dimensional spatial resolution made it possible to record low-intensity spectra of multiply charged ions in laser and Z-pinch plasmas. The method provides exceptional spectral resolution λ/Δλ ≈ 6000–10 000 in a wide spectral range (0.15–1.8 nm).

We have measured the polarization purity of undulator radiation at 12.9 keV, with hitherto unachievable precision. We could measure a polarization purity of 1.8 × 10−4 by using a silicon channel-cut crystal with six Bragg reflections at 45° as analyzer.

Non-thermal melting of semiconductor crystals, phase transitions on a sub-picosecond time scale can be studied by optical pump x-ray probe experiments. Powerful femtosecond lasers deliver brilliant ultrashort K(alpha ) pulses on a time scale from 100 fs to 1 ps that can be optimized for these pump-probe experiments. These experiments consist of two diffracting elements: (i) a bent crystal imaging the flash x-ray source in a narrow spectral window; and (ii) the sample crystal diffracting the ultrashort x-ray pulse. As penetration depths of optical pump beam are usually much shorter than x-ray extinction depths, best sensitivity to ultrafast structural changes is obtained for minimum x-ray extinction depths. This can be achieved by selecting samples containing heavy elements, thin crystalline film samples and by using asymmetric Bragg reflections, respectively. Several theoretical codes have been developed to optimize design of the instruments. X-ray topographic cameras and diffractometers were modified for fabrication and characterization of 2D bent crystals. Best practical results were obtained when structurally perfect wafers of Si, Ge, and quartz crystals were prepared while monitored by x-ray topography and diffractometry. After a final check of x-ray imaging and reflection properties of the toroidal crystals, monochromatic x-ray beam and laser pump beam are adjusted spatially to coincide on the sample crystal. Because converging x-rays impinge on the sample crystal, its rocking curve can be registered as a spatial distribution on the detector. In comparison to synchrotron experiments where about 104 pulses must be integrated, in these experiments rocking curves can be recorded in a single or in a few laser shots. Ultrafast processes are studied in Langmuir Blodgett films containing Cd, in bulk semiconductors, such as InSb, and in CdTe semiconductor films. Focused, pulsed monochromatic x-rays have been transmitted through biological samples to register many reflections, which opens the way to ultrafast studies in structural biology.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Simultaneous measurements of the integrated reflectivity of a mica crystal for different orders of reflection have been performed at a predefined Bragg angle of 45 degree(s) with use of a new method. The method is less time consuming than previous techniques and provides data with small statistical errors. It can be readily used for the calibration of x-ray crystal spectrometers. The paper presents experimental results for Bragg reflections up to the 22nd order. The obtained experimental results are compared with theoretical predictions.

Crystallographic and dispersion characteristics of muscovite at different reflection orders (2 divided by 24) for (001) lattice planes were investigated theoretically. Measurements of integral reflectivity were done for (10 divided by 38) reflection orders by using Cu and Mo X- tube radiation. Experimental results were compared with calculations for perfect and mosaic crystals. The integrated reflectivity for spherically bent mica crystals with R equals 100 and 186 mm have been calculated for various reflection orders. The results of these calculations show that muscovite crystals can be used in high reflection orders for high-resolution spectroscopy only if the crystal perfection is high enough, which provides the narrow reflection curve widths. These theoretical considerations are supported by results obtained in various plasma spectroscopic experiments. Nearly perfect muscovite crystals have been shown by using Lang and section topographic techniques for both flat and spherically bent muscovite crystals respectively. The high-quality of such crystals was also demonstrated using the scheme of obtaining a `parallel' x-ray beam and x-ray microscope schemes. Possible applications of high-quality muscovite spherical crystals are discussed.

Characterization of bent crystals used in x-ray spectroscopic instrumentation is carried out, which includes different methods for measuring the reflection curves of bent crystals and integrated reflectivities. The integrated reflectivities of a cylindrically bent PET crystal within the wavelength range of 0.3 - 0.8 nm are presented. The measured data are compared with calculations using both kinematic and dynamic theories. Based upon the x-ray dynamic theory of bent crystals, the optimal selection of the x-ray wavelength, crystal reflections and bending radius, which are necessary to observe the fine details of the reflection curve, are determined. To obtain both the energy band and the angular width of the probing beam in the order of 10-5 radian, a double-crystal spectrometer in a dispersive configuration, which consists of quartz (20.3) symmetric and silicon (111) asymmetric reflections, is suggested. As a result, the former has a nearly normal incident case, which makes possible a (Delta) (lambda) /(lambda) value of approximate 2 X 10-5; the latter reflection contributes mainly to the reduction of the angular width of the diffracted beam. A rotating device with high angular precision to measure the reflection curve is discussed.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We have performed an analyzer crystal based phase contrast imaging (ABI) experiment using a rotating anode x-ray source. The use of such an incoherent source demonstrates the potential of ABI as a quantitative characterization tool for the laboratory environment. A phase contrast image of a plastic phantom was recorded on high resolution x-ray film and the projected thickness was retrieved from a single image. The projected thickness recovered from the phase contrast image was shown to quantitatively agree with a reference optical microscope measurement.

A double crystal diffractometer (DCD) for testing LiF crystals is presented. It is possible to distinguish in a relatively short measuring time (nearly 10 minutes including change of sample and adjustment) between crystals with block desorientation angles >1′ and ≦ 1′ (1′ = 0.291 · 10−3 rad). The extention of area registered during a measurement depends on the kind of section of crystal and the kind of reflection; at the examination of {100}-cleavage faces of LiF an elliptical area of a height of 15 mm and a length of 115 mm is registered.

A system of two crystal spectrometers for accurate wavelength measurements of hard X-rays emitted by heavy ions in flight is presently being completed. The configuration is working in the focusing compensated asymmetric laue (FOCAL) mode along with high performance two-dimensional position sensitive micro-strip Ge detectors. Recent tests of the spectrometer have been performed securing quantitatively spectral resolving power and efficiency predicted by numerical simulations. For the proposed application, nearly perfect Silicon single crystals need to be bent cylindrically using a precision crystal-bending device, close to the limit where they start to break.