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In this work, we measure and model tilted x-ray refractive lenses to investigate their effects on an x-ray beam. The modelling is benchmarked against at-wavelength metrology obtained with x-ray speckle vector tracking experiments (XSVT) at the BM05 beamline at the ESRF-EBS light source, showing very good agreement. This validation permits us to explore possible applications of tilted x-ray lenses in optical design: we demonstrate that tilting 1D lenses around their focusing direction can be used for fine-tuning their focal length with possible applications in beamline optical design., Comment: 15 pages, 13 figures, 38 references to be submitted to Optics Express

We describe the development of specific measurement protocols to improve the accuracy of surface metrology of x-ray mirrors using a dedicated commercial instrument based on wavefront sensing techniques. This instrument, SHARPeR, uses measurements from a Shack–Hartmann wavefront sensor combined with a sub-aperture stitching method to provide two-dimensional maps of the surface slope errors and can measure curved mirrors above 1 m radii. In this paper, we describe the results of measurement methods developed on a SHARPeR system installed at the European Synchrotron (ESRF) to reduce the contribution of systematic errors to measurements of strongly curved spherical and aspherical x-ray mirrors with intrinsic slope errors of the order of 100–200 nrad rms. We demonstrate how this commercial integrated instrument can provide measurements of these mirrors with comparable accuracy to those measured with a long trace profiler.

The surface figure error of a hard X-ray mirror was improved by combining differential deposition and off-line metrology tools. Thin Cr layers were deposited on flat substrates by DC magnetron sputtering. The substrates were moved in front of a beam-defining aperture. The required velocity profile was calculated using a deconvolution algorithm. The Cr thickness profiles were measured directly using hard X-ray reflectivity data. The surface figure was characterized using conventional visible-light metrology instrumentation (long trace profiler) before and after the deposition. The method converges quickly, and after two iterations the mirror surface figure had improved by a factor of 7. The surface roughness evolves with increasing Cr thickness and deteriorates the quality of subsequent multilayer coatings. The mirror curvature can change upon coating, which complicates the interpretation of the surface metrology data. In this context, the role of layer stress is discussed. Potential improvements of the process are also proposed.

We present high quality bi-concave 2D focusing diamond x-ray lenses of apex-radius $R=100~\mu$m produced via laser-ablation and improved via a mechanical polishing process. Both for polished and unpolished individual lenses and for stacks of 10 lenses, we show the remaining figure errors determined using x-ray speckle tracking and compare these results to those of commercial $R=50~\mu$m beryllium lenses that have similar focusing strength and physical aperture. For two stacks of 10 diamond lenses (polished and unpolished) and a stack of 11 beryllium lenses, we present measured 2D beam profiles out of focus and wire scans to obtain the beam size in the focal plane. These results are complemented with small angle x-ray scattering (SAXS) measurements of a polished and an unpolished diamond lens. Again, we compare this to the SAXS of a beryllium lens. The polished x-ray lenses show similar figure errors to commercially available Be lenses. While the beam size in the focal plane is comparable with that of the Be lenses, the SAXS signal of the polished diamond lenses is considerably lower., Comment: 12 pages, 19 figures, 2 tables

The advent of 4$^\text{th}$ generation high-energy synchrotron facilities (ESRF-EBS and the planned APS-U, PETRA-IV and SPring-8 II) and free-electron lasers (Eu-XFEL and SLAC) allied with the recent demonstration of high-quality free-form refractive optics for beam shaping and optical correction has revived interest in compound refractive lenses (CRLs) as optics for beam transport, probe formation in X-ray micro- and nano-analysis as well as for imaging applications. Ideal CRLs have long been made available in the 'Synchrotron Radiation Workshop' (SRW), however, the current context requires more sophisticated modelling of X-ray lenses. In this work, we revisit the already implemented wave-optics model for an ideal X-ray lens in the projection approximation and propose modifications to it as to allow more degrees of freedom to both the front and back surfaces independently, which enables to reproduce misalignments and manufacturing errors commonly found in X-ray lenses. For the cases where simply tilting and transversely offsetting the parabolic sections of a CRL is not enough, we present the possibility of generating the figure errors by using Zernike and Legendre polynomials or directly adding metrology data to the lenses. We present the effects of each new degree of freedom by calculating their impact on point spread function and the beam caustics., Comment: 14 pages, 10 figures. Document sent to Proc. SPIE 11493, Advances in Computational Methods for X-Ray Optics V, 11493-17

The ID32 Soft X-ray Beamline line is an ESRF upgrade beamline for X-ray absorption (XAS) and Resonant Inelastic X-ray Scattering (RIXS) spectroscopic studies. It was opened to Users in October 2014 and provides polarised soft X-rays in the 400–1600 eV energy range. It has two branches: One branch has been designed for X-ray magnetic dichroism experiments, both linear (XMLD) and circular (XMCD), with high sensitivity, reproducibility, flexibility, user friendliness and the capability for fast energy scanning. The X-ray beam is available in two experimental areas, one with a dedicated superconducting high field magnet and a sample preparation facility, the second area being open for User instruments. The other branch is dedicated to very high energy resolution Resonant Inelastic X-ray Scattering experiments with a combined resolving power up to 30 000 around 930 eV. A scattering arm which is continuously variable under UHV vacuum over 100 degrees and a four-circle sample goniometer allows accurate positioning of the sample to enable 3D mapping of q space. Combined with the possibility of polarisation analysis of the outgoing photons the beamline provides a state-of-the-art soft X-ray RIXS facility.

Differential deposition techniques were applied to reduce the figure error of x-ray mirrors. Cr layers were sputtered on flat substrates that were moved with variable speed in front of a beam defining aperture. The required velocity profile was calculated using a deconvolution algorithm. The Cr thickness profiles were derived in two ways: directly, using x-ray reflectivity and indirectly, by measuring the surface figure before and after the deposition. After two iterations the mirror surface figure could be improved by almost one order of magnitude. This work will describe the experimental techniques and discuss the achieved accuracy. It will also address open questions such as layer stress, roughness evolution, and limitations of the available instrumentation.

X-ray near-field speckle-based phase-sensing approaches provide efficient means to characterise optical elements. Here, we present a theoretical review of several of these speckle methods in the frame of optical characterisation and provide a generalization of the concept. As we also demonstrate experimentally in another paper, the methods theoretically developed here can be applied with different beams and optics and within a variety of situations where at-wavelength metrology is desired. By understanding the differences between the various processing methods, it is possible to find and implement the best suited approach for each metrology scenario., Comment: 10 pages, 3 figures, 1 table

In a previous paper, we reviewed theoretically some of the available processing schemes for X-ray wavefront sensing based on random modulation. We here show experimental applications of the technique for characterising both refractive and reflective optical components. These fast and accurate X-ray at-wavelength metrology methods can assist the manufacture of X-ray optics that transport X-ray beams with minimum amount of wavefront distortion. We also recall how such methods can facilitate online optimization of active optics., 13 pages, 13 figures. arXiv admin note: substantial text overlap with arXiv:1902.09418

Optical metrology and polishing techniques are continuously evolving to satisfy the increasingly stringent specifications required for X-ray optical components for synchrotron and free-electron laser light source beamlines. For both spherical and aspherical geometries, the most demanding applications may have target residual figure errors close to 1 nm. To achieve such specifications and maintain them in the optomechanical mount, it is critical to develop methods capable of measuring the topography of the optical surface over the clear aperture of the mirror. The European Synchrotron Radiation Facility optical metrology laboratory has developed a stitching tool initially aimed at measuring long flat mirrors up to 1 m long with a Fizeau interferometer. The system is routinely used providing 2D maps of the optical surface. The instrument capabilities have been extended to characterize moderately curved optics using a transmission flat element, and results obtained on a high quality spherical mirror with 120 m of radius of curvature are presented. As a novel approach of stitching application, the technique has been used to improve the measurement accuracy of the Fizeau interferometer when measuring short plane mirrors. Acquisition of 2D topographies on a short plane mirror by micro-stitching interferometry is also presented and discussed.

Compound refractive lenses (CRL) offer outstanding potential for probe formation in X-ray micro- and nano-analysis as well as for imaging applications, but effective aberration-free focusing of X-rays is a key consideration when high spatial resolution and intensities are required. Available refractive optics have non-negligible aberrations which degrade their final performance. We describe a framework based on physical-optics for simulating the effect of imperfect CRL upon an X-ray beam, taking into account measured phase errors obtained from at-wavelength metrology. We model, with increasing complexity, a CRL stack as a single thin phase element, then as a more realistic compound-element including absorption and thickness effects and finally, we add realistic optical imperfections to the CRL. Coherent and partially-coherent simulations using the "Synchrotron Radiation Workshop" (SRW) are used to evaluate the different models, the effects of the phase errors and to check the validity of the design equations and suitability of the figures of merit., Comment: 14 pages, 10 figures, 5 tables

The advent of high-brightness X-ray light sources has provided the impetus for the development of focusing systems capable of yielding spatially resolved information from samples at length scales below 10 nm. Beams of such dimensions are fundamental elements in a range of instruments providing powerful analytical tools for a broad range of scientific domains including life, materials, chemical, environmental, and physical sciences. At the ESRF, particular efforts have been made towards the design and implementation of reflective optical systems capable of routine nanoprobe formation at hard X-ray wavelengths (0.1 nm and below) with resolutions in the sub-50 nm range. Often, one of the principal driving forces for the use of such systems is the capacity of reflective optics to deliver very high photon fluxes to the sample. For imaging applications at the ESRF, monochromatic photon fluxes in excess of 108ph/s/nm2 are achievable at energies above 15keV—typically 1–2 orders of magnitude greater than accessibl...

X-ray mirror figure errors are commonly measured in the synchrotron community using Long Trace Profiler (LTP) or Nanometer Optical measuring Machine (NOM) instruments, both providing 2D slope measurement. 3D reconstruction is possible but time consuming, and requires a high stability of environmental conditions over long periods which is not easy to achieve. Characterisation of the complete topography of the mirror surface is essential for the application of deterministic figure correction techniques and also to reveal undesired stresses or deformations, such as twist, introduced by optomechanical mounting. At the ESRF metrology laboratory Fizeau stitching methods are under development. A full automated mechanical setup dedicated to stitching measurement of long flat mirrors is now operational. We have previously demonstrated accurate reconstruction by stitching 2D profiles acquired from Fizeau subaperture measurements. This work is focused on 3D reconstruction of flat mirror surfaces up to one meter long. Repeatability, accuracy and in particular the influence of the transmission element will be discussed.

X-ray mirror quality has continuously improved over the past 20 years and manufacturers are now able to provide long mirrors with slope errors below 0.2 μrad. Nevertheless, these mirrors are mounted on holders or even mechanical benders to adjust their curvature and their intrinsic quality must be preserved from any parasitic deformation such as twist. The most direct method of detecting these deformations is to measure the 3D topography of the optical surface. At the ESRF metrology laboratory, three different stitching systems are under development based on Fizeau sub-aperture measurements. The first one consists of measuring long flat mirrors, the second based on the relative angle determinable stitching interferometry (RADSI) method developed at SPring-8 is aimed primarily at the measurement of short mirrors with strong curvature down to a few meters, and the last, also based on the RADSI method, is dedicated to characterize longer mirrors with intermediate curvature. For each method we will describe the measurement setup and discuss first results obtained. Micro-stitching interferometry is also currently used at the ESRF metrology laboratory. The technique is suitable for measuring deeply curved aspherical profiles and will be illustrated with results from a Kirkpatrick-Baez mirror system for nano-focusing.

ID16B is a versatile hard X-ray nanoprobe devoted to X-ray nano-analysis. It combines X-ray fluorescence, X-ray diffraction, X-ray absorption spectroscopy and 2D/3D X-ray imaging techniques., Within the framework of the ESRF Phase I Upgrade Programme, a new state-of-the-art synchrotron beamline ID16B has been recently developed for hard X-ray nano-analysis. The construction of ID16B was driven by research areas with major scientific and societal impact such as nanotechnology, earth and environmental sciences, and bio-medical research. Based on a canted undulator source, this long beamline provides hard X-ray nanobeams optimized mainly for spectroscopic applications, including the combination of X-ray fluorescence, X-ray diffraction, X-ray excited optical luminescence, X-ray absorption spectroscopy and 2D/3D X-ray imaging techniques. Its end-station re-uses part of the apparatus of the earlier ID22 beamline, while improving and enlarging the spectroscopic capabilities: for example, the experimental arrangement offers improved lateral spatial resolution (∼50 nm), a larger and more flexible capability for in situ experiments, and monochromatic nanobeams tunable over a wider energy range which now includes the hard X-ray regime (5–70 keV). This paper describes the characteristics of this new facility, short-term technical developments and the first scientific results.

A new figuring station was designed and installed at the ESRF beamline BM05. It allows the figuring of mirrors within an iterative process combining the advantage of online metrology with dry etching. The complete process takes place under a vacuum environment to minimize surface contamination while non-contact surfacing tools open up the possibility of performing at-wavelength metrology and eliminating placement errors. The aim is to produce mirrors whose slopes do not deviate from the stigmatic profile by more than 0.1 µrad rms while keeping surface roughness in the acceptable limit of 0.1-0.2 nm rms. The desired elliptical mirror surface shape can be achieved in a few iterations in about a one day time span. This paper describes some of the important aspects of the process regarding both the online metrology and the etching process.

The ESRF metrology laboratory has recently acquired a new optical micro-interferometer optimised for micro-roughness measurement of X-ray mirrors. The fully integrated system offers a wide range of measurement capabilities adapted for both very rough surfaces and super smooth surfaces ( First we give an overview of the performance of the instrument in terms of accuracy and repeatability. Subsequently we present the stitching option, how to handle it to improve accuracy, indicating some limits and approaches to overcome difficulties. Finally, we compare profiles obtained by micro-stitching interferometry with those measured using a long trace profiler.

For nearly 20 years, the X-ray Optics Group of the ESRF has been playing a major role in the development of new X-ray optical systems, many of which are widely used at synchrotrons around the globe.

The upgraded ESRF end station ID16A was equipped with a new Kirkpatrick-Baez (KB) nano-focusing setup. The figured KB mirrors were coated with steeply graded W/B4C multilayers to account for the variable angle of reflection along the beam footprint. The multilayers were deposited at the ESRF Multilayer Facility by DC magnetron sputtering in dynamic mode, where the substrates move in front of the sputter cathodes. The present work deals with the design, the fabrication, and the characterization of the coatings. First results obtained during commissioning experiments on ID16A complement the report.

In this study we present the potentialities of CVD diamond as an ionisation chamber for radiotherapy applications. Trapping levels present in CVD diamond are characterised using Thermally Stimulated Current (TSC) method with X-ray sources. The influence of the corresponding defects on the detector response is investigated and compared to those observed in natural diamond. Also, their spatial distribution across a large area polycrystalline diamond ionisation chamber is discussed. Results show the relative influence of two different populations of trapping levels in CVD diamond whose effect is crucial for radiotherapy applications. To partially overcome the defect detrimental effects, we propose to use CVD diamond ionisation chambers at moderate temperatures from 70 to 100 °C that could be provided by self heating of the device, for a dramatically improved stability and reproducibility.

To investigate the influence of intrinsic defects in polycrystalline CVD diamond, we have used a micro-focused X-ray beam to induce local photo-currents in solid state ionisation chambers. The device behaviour was studied as a function of the defect level populations. This microscopic study of the X-ray sensitivity was then performed using varying initial states of the devices as well as varying device temperatures. These measurements, coupled with the study of the temporal evolution of the photocurrent as a function of the temperature, seemed to demonstrate the existence of highly localised regions that may detrimentally affect the overall device response. This may demonstrate that the imperfections CVD diamond devices exhibit may be caused by extremely localised point defects.

High accuracy beamline instruments have been designed and developed for 12 years at the ESRF with an increasing demand of static and dynamic qualities. Over the last five years, microscopy beamlines, and more generally, the need for micro positioning when using small X-ray beams, has been a driving force for improving instrument compactness when combining movements, and a consequence has lead to a high level of intricacy. Even if resolutions of 0.1 μm, and high quality guiding (70 μrd), are easily found in commercially available translation stages, overall sizes and lever arms can lead to larger spheres of confusion. Moreover, environmental considerations such as vacuum compatibility can further restrict the choice of appropriate translations. To meet the various needs of the micro-focusing beamlines, compact and high-resolution micro-jacks, and xyz vacuum compatible cross tables have been developed in-house. A series of standard low profile components such as elevators (1 μm10mm), μ rotary tables (Laue angle rocking curve), sample slits, inserted with either pico motors or stepper Hacks are now available. Using this approach an integrated all in one experimental station was designed for X-ray microscopy beamlines, like the scanning X-ray microscope for ID21, (10 sub-micron axes operated at 10-6mbars). Other versions are currently being developed for micro-fluorescence beamlines or post monochromators. The development programme has benefited greatly from the presence of the ESRF precision engineering laboratory (PEL), which allowed high quality metrology measurements to be performed on both the prototype and the final systems.

Diamond is a semiconducting material which can withstand high temperatures, a wide range of corrosive environments and exhibits high radiation hardness. This combination of properties makes it extremely attractive for use as photon and particle detectors. The ESRF ID21 SXM has been used to image the spatial variations of detector sensitivity over a range of both natural and Chemical Vapour Deposited (CVD) diamond devices. The measurements are performed by mapping the photon-induced current flow of the biased detectors. Evaluation of the sensitivity inhomogeneities are of dual interest. For detection applications involving relatively small beams it is important that the device response be as uniform as possible. Furthermore, from a fundamental aspect, the understanding of the origin of the sensitivity variations can be a route, for example in CVD materials, to modifying the growth and processing parameters in order to produce improved devices. This paper demonstrates an application of alternative detection modes in X-ray microscopy for a problem of technological interest. Moreover, it shows how the flexible control of the primary X-ray penetration depth by varying the probe energy permits an evaluation of the relative influence of the surface and bulk material.

Anisotropic elasticity of single-crystal silicon, applications to modelling of a bent X-ray mirror, and thermal deformation of a liquid-nitrogen-cooled monochromator crystal are presented., The crystal lattice of single-crystal silicon gives rise to anisotropic elasticity. The stiffness and compliance coefficient matrix depend on crystal orientation and, consequently, Young’s modulus, the shear modulus and Poisson’s ratio as well. Computer codes (in Matlab and Python) have been developed to calculate these anisotropic elasticity parameters for a silicon crystal in any orientation. These codes facilitate the evaluation of these anisotropy effects in silicon for applications such as microelectronics, microelectromechanical systems and X-ray optics. For mechanically bent X-ray optics, it is shown that the silicon crystal orientation is an important factor which may significantly influence the optics design and manufacturing phase. Choosing the appropriate crystal orientation can both lead to improved performance whilst lowering mechanical bending stresses. The thermal deformation of the crystal depends on Poisson’s ratio. For an isotropic constant Poisson’s ratio, ν, the thermal deformation (RMS slope) is proportional to (1 + ν). For a cubic anisotropic material, the thermal deformation of the X-ray optics can be approximately simulated by using the average of ν12 and ν13 as an effective isotropic Poisson’s ratio, where the direction 1 is normal to the optic surface, and the directions 2 and 3 are two normal orthogonal directions parallel to the optical surface. This average is independent of the direction in the optical surface (the crystal plane) for Si(100), Si(110) and Si(111). Using the effective isotropic Poisson’s ratio for these orientations leads to an error in thermal deformation smaller than 5.5%.

The presence of impurities in natural diamond detectors and their influence on the detection properties have been investigated. A micrometer size X-ray beam generated by a synchrotron light source as well as collimated alpha particles were used to probe the effects induced by non isotropic distributions of defects on diamond detector characteristics. A strong correlation clearly appears between the measured photocurrent maps and the X-ray induced luminescence pictures. Spatially resolved alpha measurements are compared to local infrared and ultraviolet absorption measurements and demonstrate the influence of defects on local and global diamond detection spectra.

Some aspects of the dislocation contrast observed at third-generation synchrotron radiation set-ups are presented. They can be explained by taking into account angular deviation effects on the beam propagation, which are visible because of the ;almost plane-wave' character of these sources. In particular, we show how the evolution of the direct image width of a dislocation as a function of the sample-to-film distance can allow a complete determination of the Burgers vector, i.e. in sign and modulus. In addition, experimental results obtained in monochromatic beam topography are compared with simulated images calculated assuming plane-wave illumination and are demonstrated to show a satisfactory agreement. The utility of the weak-beam technique in enhancing the spatial resolution is demonstrated and a criterion for the selection of experimental conditions depending upon the required spatial resolution, signal-to-noise ratio and exposure time is presented.

Phase objects are readily imaged through Fresnel diffraction in the hard x-ray beams of third-generation synchrotron radiation sources such as the ESRF, due essentially to the very small angular size of the source. Phase objects can lead to spurious contrast in x-ray diffraction images (topographs) of crystals. It is shown that this contrast can be eliminated through random phase plates, which provide an effective way of tailoring the angular size of the source. The possibilities of this very simple technique for imaging phase objects in the hard x-ray range are explored experimentally and discussed. They appear very promising, as shown in particular by the example of a piece of human vertebra, and could be extended to phase tomography.

The source characteristics of third-generation synchrotron radiation machines lead to enhanced possibilities for diffraction topographic techniques: real-time observations, high-resolution experiments, investigation of heavy or bulky materials using short wavelengths and the possibility of using large sample environments. We describe the instrumentation of the ESRF ID19 'Topography and High Resolution Diffraction Beamline', which has been designed to take advantage of these new experimental possibilities. Experiments performed, in white and monochromatic beam, on two other beamlines of the ESRF illustrate these new possibilities. They show that (i) typical exposure times for white-beam topography (down to about 10-2 s) are about 102-103 times shorter than at other synchrotron radiation topographic set-ups, (ii) the divergence of the diffracted beam is small enough to retain good spatial resolution when placing the film far (up to 1 m) from the sample, (iii) with short wavelengths (about 10 pm and less) it is possible to carry out topographical investigations of bulky or heavy samples or to detect weak long-range deformation fields of defects and (iv) 'low-divergent wave' or 'weak-beam' monochromatic beam topographs can be recorded in a few seconds. Sample-heating effects are observed in white-beam topography even for materials that are not highly absorbing or thermally insulating. A simple criterion for observation of these effects is presented and tested.

International audience; The ID21 Scanning X-ray Microscope (SXM) is optimized for micro-spectroscopy with submicron resolution in the 2 to 9.5 keV energy range. After a brief description of the microscope setup, we present here recent developments, in particular, the latest version of the compact Wavelength Dispersive Spectrometer and the refurbished cryo-stage

International audience; The temperature distribution and thermal deformation of optics subject to heat load largely depend on the system geometry. It is possible to optimize this geometry and therefore to minimize thermal distortion of both white beam mirrors and multilayer-based optics. The thermal slope error in an optimized water-cooled white beam mirror can be reduced by two to three orders of magnitude compared to a non-optimized mirror

The degree of coherence preservation of x-ray multilayers was investigated using Talbot imaging on the ESRF undulator beamline ID06. Several W/B4C multilayer mirrors with differing d-spacings were studied with monochromatic light at various photon energies. To understand the respective influence of the underlying substrate and the multilayer coatings, measurements were made under total reflection, at different Bragg peaks, and on the bare substrates. In addition, samples with different substrate quality were compared. The relation between spatial coherence preservation and the visibility of characteristic line structures in the x-ray beam will be discussed.

European Synchrotron Radiation Facility (ESRF) in-house designed Kirkpatrick–Baez (KB) focusing systems have been extensively used for high efficiency beam focusing over the past years. More recently however, increasing interest in nanofocusing techniques has directed our development efforts towards more compact, higher stability designs for dynamic focusing systems in which the optimization of numerous parameters enables mirror bending approaching its mechanical limits. Simultaneously, progress in fixed focus mirror fabrication techniques – notably ion beam figuring, differential deposition and elastic emission machining – now make the fabrication of highly elliptical, fixed focus X-ray optics an interesting option. This has simplified conception (no bending mechanics) which in turn has led to the design of miniaturized KBs.A general overview of these recent developments in both dynamic bending and fixed focus KB systems is presented.

As part of phase 1 of the European synchrotron radiation facility (ESRF) upgrade programme, a new beamline (UPBL6) for the study of electronic excitations using inelastic scattering and emission spectroscopy will be designed and constructed. The new beamline will provide an intense stable X-ray beam at two different spectrometers to be used on a time-shared basis. One of the spectrometers will be dedicated to resonant inelastic X-ray scattering (RIXS); the other to X-ray Raman spectroscopy (XRS). This beamline is currently (June 2010) in the design phase and may be fully operational by early 2013.