Nested neutron microfocusing optics on SNAP

The high source intensity of the Spallation Neutron Source (SNS), together with efficient detectors and large detector solid angles, now makes possible neutron experiments with much smaller sample volumes than previously were practical. Nested Kirkpatrick–Baez supermirror optics provide a promising and efficient way to further decrease the useable neutron sample size by focusing polychromatic neutrons into microbeams. Because the optics are nondispersive, they are ideal for spallation sources and for polychromatic and wide bandpass experiments on reactor sources. Theoretical calculations indicate that nested mirrors can preserve source brilliance at the sample for small beams and for modest divergences that are appropriate for diffraction experiments. Although the flux intercepted by a sample can be similar with standard beam-guided approaches, the signal-to-background is much improved with small beams on small samples. Here we describe the design, calibration and performance of a nested neutron mirror pair for the Spallation Neutrons At Pressure (SNAP) beamline at the SNS. High-pressure neutron diffraction is but one example of a large class of neutron experiments that will benefit from spatially-resolved microdiffraction.     

High energy X-ray micro-optics

A tremendous progress in X-ray optics development was made in the past decade. Progress has been driven by the unique properties of X-ray beams produced by third generation synchrotron sources. The very low emittance coupled with high brilliance allows one to develop efficient focusing devices for new X-ray microscopy techniques. This article provides an overview of the state-of-the-art in micro-focusing optics and methods for hard X-rays. The main emphasis is put on those methods which aim to produce submicron and nanometer resolution. These methods fall into three broad categories: reflective, refractive and diffractive optics.The basic principles and recent achievements are discussed for all optical devices. To cite this article: A. Snigirev, I. Snigireva, C. R. Physique 9 (2008).     

News and Views: Two Years of the Website lightsources.org

The “Helmholtz-Zentrum für Materialien und Energie,” HZB, in Berlin looks back on a long and successful history in the development and operation of storage ring (SR)-based synchrotron radiation sources, starting in the early 1980s with BESSY I, followed by BESSY II in the late 1990s and the Metrology Light Source set up for the PTB (Physikalisch-Technische Bundesanstalt) in 2008. Novel concepts to better tailor the radiation properties of storage rings to the user's demands (e.g., for short pulses such as low alpha optics and femto-slicing facility) have been pioneered or improved at the HZB. Despite these efforts and the recent progress made in the development towards diffraction-limited SR, it seems right to look into alternative accelerator technologies providing high average current and short-pulsed (sub-ps) beams of exceptional brilliance and low energy spread without the fundamental restrictions of a beam circulating in an equilibrium state of the phase-space distribution.     

The Munich Compact Light Source: initial performance measures

While large‐scale synchrotron sources provide a highly brilliant monochromatic X‐ray beam, these X‐ray sources are expensive in terms of installation and maintenance, and require large amounts of space due to the size of storage rings for GeV electrons. On the other hand, laboratory X‐ray tube sources can easily be implemented in laboratories or hospitals with comparatively little cost, but their performance features a lower brilliance and a polychromatic spectrum creates problems with beam hardening artifacts for imaging experiments. Over the last decade, compact synchrotron sources based on inverse Compton scattering have evolved as one of the most promising types of laboratory‐scale X‐ray sources: they provide a performance and brilliance that lie in between those of large‐scale synchrotron sources and X‐ray tube sources, with significantly reduced financial and spatial requirements. These sources produce X‐rays through the collision of relativistic electrons with infrared laser photons. In this study, an analysis of the performance, such as X‐ray flux, source size and spectra, of the first commercially sold compact light source, the Munich Compact Light Source, is presented.     

Preventing carbon contamination of optical devices for X‐rays: the effect of oxygen on photon‐induced dissociation of CO on platinum

Platinum is one of the most common coatings used to optimize mirror reflectivity in soft X‐ray beamlines. Normal operation results in optics contamination by carbon‐based molecules present in the residual vacuum of the beamlines. The reflectivity reduction induced by a carbon layer at the mirror surface is a major problem in synchrotron radiation sources. A time‐dependent photoelectron spectroscopy study of the chemical reactions which take place at the Pt(111) surface under operating conditions is presented. It is shown that the carbon contamination layer growth can be stopped and reversed by low partial pressures of oxygen for optics operated in intense photon beams at liquid‐nitrogen temperature. For mirrors operated at room temperature the carbon contamination observed for equivalent partial pressures of CO is reduced and the effects of oxygen are observed on a long time scale.     

Microcrystallography using single‐bounce monocapillary optics

X‐ray microbeams have become increasingly valuable in protein crystallography. A number of synchrotron beamlines worldwide have adapted to handling smaller and more challenging samples by providing a combination of high‐precision sample‐positioning hardware, special visible‐light optics for sample visualization, and small‐diameter X‐ray beams with low background scatter. Most commonly, X‐ray microbeams with diameters ranging from 50 µm to 1 µm are produced by Kirkpatrick and Baez mirrors in combination with defining apertures and scatter guards. A simple alternative based on single‐bounce glass monocapillary X‐ray optics is presented. The basic capillary design considerations are discussed and a practical and robust implementation that capitalizes on existing beamline hardware is presented. A design for mounting the capillary is presented which eliminates parasitic scattering and reduces deformations of the optic to a degree suitable for use on next‐generation X‐ray sources. Comparison of diffraction data statistics for microcrystals using microbeam and conventional aperture‐collimated beam shows that capillary‐focused beam can deliver significant improvement. Statistics also confirm that the annular beam profile produced by the capillary optic does not impact data quality in an observable way. Examples are given of new structures recently solved using this technology. Single‐bounce monocapillary optics can offer an attractive alternative for retrofitting existing beamlines for microcrystallography.     

Fabrication of nested elliptical KB mirrors using profile coating for synchrotron radiation X-ray focusing

This paper describes fabrication methods used to demonstrate the advantages of nested or Montel optics for micro/nanofocusing of synchrotron X-ray beams. A standard Kirkpatrick-Baez (KB) mirror system uses two separated elliptical mirrors at glancing angles to the X-ray beam and sequentially arranged at 90° to each other to focus X-rays successively in the vertical and horizontal directions. A nested KB mirror system has the two mirrors positioned perpendicular and side-by-side to each other. Compared to a standard KB mirror system, Montel optics can focus a larger divergence and the mirrors can have a shorter focal length. As a result, nested mirrors can be fabricated with improved demagnification factor and ultimately smaller focal spot, than with a standard KB arrangement. The nested system is also more compact with an increased working distance, and is more stable, with reduced complexity of mirror stages. However, although Montel optics is commercially available for laboratory X-ray sources, due to technical difficulties they have not been used to microfocus synchrotron radiation X-rays, where ultra-precise mirror surfaces are essential. The main challenge in adapting nested optics for synchrotron microfocusing is to fabricate mirrors with a precise elliptical surface profile at the very edge where the two mirrors meet and where X-rays scatter. For example, in our application to achieve a sub-micron focus with high efficiency, a surface figure root-mean-square (rms) error on the order of 1 nm is required in the useable area along the X-ray footprint with a ∼0.1 mm-diameter cross section. In this paper we describe promising ways to fabricate precise nested KB mirrors using our profile coating technique and inexpensive flat Si substrates.     

Workshop Nanoscience B: Self-Assembly-from molecules to materials

In recent years, there has been growing interest in the design of electron accelerators in order to reduce beam emittance and to increase photon brilliance (from third-generation synchrotron sources to free electron lasers). This has increased the coherent properties of the beam and has opened up new branches of microscopy and spectroscopy at nanometer-length scales. The X-ray nano probe is going to be an important tool for future research, hence there has been substantial research carried out in order to develop nano focusing optics of diffraction-limited performance.     

Compact IR synchrotron beamline design

Third‐generation storage rings are massively evolving due to the very compact nature of the multi‐bend achromat (MBA) lattice which allows amazing decreases of the horizontal electron beam emittance, but leaves very little place for infrared (IR) extraction mirrors to be placed, thus prohibiting traditional IR beamlines. In order to circumvent this apparent restriction, an optimized optical layout directly integrated inside a SOLEIL synchrotron dipole chamber that delivers intense and almost aberration‐free beams in the near‐ to mid‐IR domain (1–30 µm) is proposed and analyzed, and which can be integrated into space‐restricted MBA rings. Since the optics and chamber are interdependent, the feasibility of this approach depends on a large part on the technical ability to assemble mechanically the optics inside the dipole chamber and control their resulting stability and thermo‐mechanical deformation. Acquiring this expertise should allow dipole chambers to provide almost aberration‐free IR synchrotron sources on current and `ultimate' MBA storage rings.     

Mini‐beam collimator enables microcrystallography experiments on standard beamlines

The high‐brilliance X‐ray beams from undulator sources at third‐generation synchrotron facilities are excellent tools for solving crystal structures of important and challenging biological macromolecules and complexes. However, many of the most important structural targets yield crystals that are too small or too inhomogeneous for a `standard' beam from an undulator source, ～25–50 µm (FWHM) in the vertical and 50–100 µm in the horizontal direction. Although many synchrotron facilities have microfocus beamlines for other applications, this capability for macromolecular crystallography was pioneered at ID‐13 of the ESRF. The National Institute of General Medical Sciences and National Cancer Institute Collaborative Access Team (GM/CA‐CAT) dual canted undulator beamlines at the APS deliver high‐intensity focused beams with a minimum focal size of 20 µm × 65 µm at the sample position. To meet growing user demand for beams to study samples of 10 µm or less, a `mini‐beam' apparatus was developed that conditions the focused beam to either 5 µm or 10 µm (FWHM) diameter with high intensity. The mini‐beam has a symmetric Gaussian shape in both the horizontal and vertical directions, and reduces the vertical divergence of the focused beam by 25%. Significant reduction in background was achieved by implementation of both forward‐ and back‐scatter guards. A unique triple‐collimator apparatus, which has been in routine use on both undulator beamlines since February 2008, allows users to rapidly interchange the focused beam and conditioned mini‐beams of two sizes with a single mouse click. The device and the beam are stable over many hours of routine operation. The rapid‐exchange capability has greatly facilitated sample screening and resulted in several structures that could not have been obtained with the larger focused beam.     

Phase‐space analysis and experimental results for secondary focusing at X‐ray beamlines

Micro‐focusing optical devices at synchrotron beamlines usually have a limited acceptance, but more flux can be intercepted if such optics are used to focus secondary sources created by the primary optics. Flux throughput can be maximized by placing the secondary focusing optics close to or exactly at the secondary source position. However, standard methods of beamline optics analysis, such as the lens equation or matching the mirror surface to an ellipse, work poorly when the source‐to‐optics distance is very short. In this paper the general characteristics of the focusing of beams with Gaussian profiles by a `thin lens' are analysed under the paraxial approximation in phase space, concluding that the focusing of a beam with a short source‐to‐optics distance is distinct from imaging the source; slope errors are successfully included in all the formulas so that they can be used to calculate beamline focusing with good accuracy. A method is also introduced to use the thin‐lens result to analyse the micro‐focusing produced by an elliptically bent trapezoid‐shaped Kirkpatrick–Baez mirror. The results of this analysis are in good agreement with ray‐tracing simulations and are confirmed by the experimental results of the secondary focusing at the 18‐ID Bio‐CAT beamline (at the APS). The result of secondary focusing carried out at 18‐ID using a single‐bounce capillary can also be explained using this phase‐space analysis. A discussion of the secondary focusing results is presented at the end of this paper.     

Protective radiolucent aluminium oxide coatings for beryllium X‐ray optics

Beryllium, being one of the most transparent materials to X‐ray radiation, has become the material of choice for X‐ray optics instrumentation at synchrotron radiation sources and free‐electron laser facilities. However, there are concerns due to its high toxicity and, consequently, there is a need for special safety regulations. The authors propose to apply protective coatings in order to seal off beryllium from the ambient atmosphere, thus preventing degradation processes providing additional protection for users and prolonging the service time of the optical elements. This paper presents durability test results for Be windows coated with atomic‐layer‐deposition alumina layers run at the European Synchrotron Radiation Facility. Expositions were performed under monochromatic, pink and white beams, establishing conditions that the samples could tolerate without radiation damage. X‐ray treatment was implemented in various environments, i.e. vacuum, helium, nitrogen, argon and dry air at different pressures. Post‐process analysis revealed their efficiency for monochromatic and pink beams.     

X radiation sources based on accelerators

Light sources based on accelerators aim at producing very high brilliance coherent radiation, tuneable from the infrared to X-ray range, with picosecond or femtosecond light pulses.The first synchrotron light sources were built around storage rings in which a large number of relativistic electrons produce “synchrotron radiation” when their trajectory is subjected to a magnetic field, either in bending magnets or in specific insertion devices (undulators), made of an alternating series of magnets, allowing the number of curvatures to be increased and the radiation to be reinforced.These “synchrotron radiation” storage rings are now used worldwide (there are more than thirty), and they simultaneously distribute their radiation to several tens of users around the storage ring.The most effective installations in term of brilliance are the so-called 3rd generation synchrotron radiation light sources. The radiation produced presents pulse durations of the order of a few tens of ps, at a high rate (of the order of MHz); it is tuneable over a large range, depending on the magnetic field and the electron beam energy and its polarisation is adjustable (in the VUV-soft-X range). Generally, a very precise spectral selection is made by the users with a monochromator.The single pass linear accelerators can produce very short electron bunches (). The beam of very high electronic density is sent into successive undulator modules, reinforcing the radiation's longitudinal coherence, produced according to a Free Electron Laser (FEL) scheme by the interaction between the electron bunch and a light wave. The very high peak brilliance justifies their designation as 4th generation sources. The number of users is smaller because an electron pulse produces a radiation burst towards only one beamline. Energy Recovery Linacs (ERL) let the beam pass several times in the accelerator structures either to recover the energy or to accelerate the electrons during several turns, and thus provide subpicosecond beams for a greater number of users.A state-of-the-art of X sources using conventional (and not laser plasma based) accelerators is given here, underlying the performance already reached or forecast and the essential challenges. To cite this article: M.-E. Couprie, J.-M. Filhol, C. R. Physique 9 (2008).     

A new optical scheme for large‐extraction small‐aberration vacuum‐ultraviolet synchrotron radiation beamlines

Vacuum‐ultraviolet radiation delivered by bending‐magnet sources is used at numerous synchrotron radiation facilities worldwide. As bending‐magnet radiation is inherently much less collimated compared with undulator sources, the generation of high‐quality intense bending‐magnet vacuum‐ultraviolet photon beams is extremely demanding in terms of the optical layout due to the necessary larger collection apertures. In this article, an optimized optical layout which takes into account both the optical and electron beam properties is proposed. This layout delivers an improved beam emittance of over one order of magnitude compared with existing vacuum‐ultraviolet bending‐magnet beamlines that, up to now, do not take into account electron beam effects. The arrangement is made of two dedicated mirrors, a cylindrical and a cone‐shaped one, that focus independently both the horizontal and the vertical emission of a bending‐magnet source, respectively, and has been already successfully applied in the construction of the infrared beamline at the Brazilian synchrotron. Using this scheme, two vacuum‐ultraviolet beamline designs based on a SOLEIL synchrotron bending‐magnet source are proposed and analysed. They would be useful for future upgrades to the DISCO beamline at SOLEIL and could be readily implemented at other synchrotron radiation facilities.     

X‐ray microscopy at the advanced photon source

In modern third generation synchrotron sources, undulators have become the principal source of X-rays and today a brilliance close to 10²¹ photons/sec?mm²?mrad?0.1%BW is routinely attained for photon energies of 10 keV. However, generating brilliant beams of photons with energies of 50 keV and above leads to conflicting choices for the undulator parameters as the following analysis shows.     

Optimized IR synchrotron beamline design

Synchrotron infrared beamlines are powerful tools on which to perform spectroscopy on microscopic length scales but require working with large bending‐magnet source apertures in order to provide intense photon beams to the experiments. Many infrared beamlines use a single toroidal‐shaped mirror to focus the source emission which generates, for large apertures, beams with significant geometrical aberrations resulting from the shape of the source and the beamline optics. In this paper, an optical layout optimized for synchrotron infrared beamlines, that removes almost totally the geometrical aberrations of the source, is presented and analyzed. This layout is already operational on the IR beamline of the Brazilian synchrotron. An infrared beamline design based on a SOLEIL bending‐magnet source is given as an example, which could be useful for future IR beamline improvements at this facility.     

Geometrical and wave optics of paraxial beams

Most calculational techniques used to evaluate beam propagation are geared towards either fully coherent or fully incoherent beams. The intermediate partial-coherence regime, while in principle known for a long time, has received comparably little attention so far. The resulting shortage of adequate calculational techniques is currently being felt in the realm of x-ray optics where, with the advent of third generation synchrotron light sources, partially coherent beams become increasingly common. The purpose of this paper is to present a calculational approach which, utilizing a "variance matrix" representation of paraxial beams, allows for a straightforward evaluation of wave propagation through an optical system. Being capable of dealing with an arbitrary degree of coherence, this approach covers the whole range from wave to ray optics, in a seamless fashion.     

One way only to synchrotron light sources upgrade?

The last decade has seen a renaissance of machine‐physics studies and technological advancements that aim to upgrade at least 15 synchrotron light sources worldwide to diffraction‐limited storage rings. This is expected to improve the average spectral brightness and transversally coherent fraction of photons by several orders of magnitude in the soft‐ and hard‐X‐ray wavelength range, at the expense of pulse durations longer than ～80 ps FWHM. This paper discusses the compatibility of schemes for the generation of sub‐picosecond photon‐pulse durations in synchrotron light sources with standard multi‐bunch user operation and, in particular, diffraction‐limited electron optics design. The question of this compatibility is answered taking into consideration the storage ring beam energy and the constraint of existing synchrotrons' infrastructure. An alternative scheme for the upgrade of medium‐energy synchrotron light sources to diffraction‐limited storage rings and the simultaneous production of picosecond‐long photon pulses in a high‐gain free‐electron laser scheme are illustrated.     

The high‐resolution diffraction beamline P08 at PETRA III

The new third‐generation synchrotron radiation source PETRA III located at the Deutsches Elektronen‐Synchrotron DESY in Hamburg, Germany, has been operational since the second half of 2009. PETRA III is designed to deliver hard X‐ray beams with very high brilliance. As one of the first beamlines of PETRA III the high‐resolution diffraction beamline P08 is fully operational. P08 is specialized in X‐ray scattering and diffraction experiments on solids and liquids where extreme high resolution in reciprocal space is required. The resolving power results in the high‐quality PETRA III beam and unique optical elements such as a large‐offset monochromator and beryllium lens changers. A high‐precision six‐circle diffractometer for solid samples and a specially designed liquid diffractometer are installed in the experimental hutch. Regular users have been accepted since summer 2010.