Kirkpatrick-Baez Mirrors Research Articles

Status and Developments of BL13-XALOC, the macromolecular crystallography beamline at Alba

BL13-XALOC is a Macromolecular Crystallography beamline at the newly built 3-GeV synchrotron ALBA (Barcelona). The optics design is based on an in-vacuum undulator, a Si(111) channel-cut crystal monochromator, and a pair of KB mirrors. The optical design allows three main operation modes: an unfocused configuration, where one or both mirrors are removed from the photon beam path; a focused configuration, where both mirrors can focus the beam to 49×9 μm2 FWHM (H×V), and a defocused configuration that can match the size of the beam to the dimensions of the crystals or to focus it at the detector. To achieve a uniform defocused beam, the slope errors were reduced by using novel method together with our high-accuracy metrology laboratory. Thorough commissioning has also demonstrated that the X-ray beam has excellent energy and spatial stability. The End Station includes a high accuracy single axis diffractometer, a removable mini-kappa goniometer, an automated sample mounting robot and a Pilatus6M, photon-counting detector. This equipment, together with the operation flexibility, allows the beamline to tackle a large variety of crystals, from medium sized crystals with large unit cell parameters to microcrystals. Several examples of high-quality data collections measured during beamline commissioning are described. The beamline started user operation on 18th July 2012.

PROXIMA 2A – A New Fully Tunable Micro-focus Beamline for Macromolecular Crystallography

PROXIMA 2 is the first canted beamline at the French National Synchrotron Source SOLEIL, and it will provide two independent and tunable experimental stations, PX2-A & PX2-B, dedicated to macromolecular crystallography. The first station, PX2-A, is currently under construction. The source is an in-vacuum U24 undulator, and the optical layout includes a cryogenically cooled channel-cut Si[111] monochromator, a convex horizontal pre-focussing mirror (HPM) and a pair of focusing bimorph mirrors in Kirkpatrick-Baez (KB) configuration. This innovative optical scheme, harnesses a convex mirror to produce a virtual secondary source, which permits the KB mirrors to refocus the X-rays down to 5 μm from a relatively large horizontal source size. In fully focussed mode, the cross-section of the beam at the sample position will be approximately 5.0 μm × 3.5 μm (H×V FWHM) delivering a photon flux of 1×1013 – 4×1011 ph/s over the range of 5 – 15 keV with a desired positional stability better than 0.5 μm rms over several hours. To achieve such stability, the supports for the optical elements are designed to minimise the effects of vibrations transmitted from the surroundings, and accelerometers will be mounted in situ to monitor these effects. For long term drifts, the experimental hutch is temperature controlled to within 0.1°C, and a preparation laboratory acts as a buffer zone. Two types of X-ray Beam Position Monitors (XBPMs), single crystal CVD diamond and thin foil-diode devices, have been developed to improve their robustness and signal-noise ratio. Due to the limitations of space, three compact and modular "slit boxes" have been designed: These vessels house a variety of beam conditioning elements such as slits, XBPMs, attenuators, imagers and a fast shutter. At the end of the station, a micro-diffractometer and an area detector (ADSC Q315) have already been installed, and the first X-ray diffraction data with unfocussed beam from test crystals are of excellent quality.

Bendable Kirkpatrick-Baez mirrors for the ALS micro-diffraction beamline 12.3.2: optimal tuning and alignment for multiple focusing geometries

Using an example of Kirkpatrick-Baez mirrors for the micro-diffraction beamline 12.3.2, we present the recent development of bendable x-ray optics and experimental techniques used for focusing of beams of soft and hard x-rays at the Advanced Light Source (ALS). We briefly review the nature of the bending and analyze a generalized solution of the bending equation for a side-profiled elliptically bent mirror substrate. A scaling rule is derived to understand a range of reliable tunability of the bendable optics for different applications (e.g., different focal distances and grazing incidence angles). Original design approaches are developed for assembly of bendable mirrors with minimal spurious stress and misalignment and for final precision compensation of the residual stress, substrate twist, and roll-off misalignment of the mirrors. Procedures used for optimal shaping and alignment of bendable optics at the ALS optical metrology laboratory are also briefly reviewed.

Experimental methods for optimal tuning of bendable mirrors for diffraction-limited soft x-ray focusing

We report on hands-on experimental methods developed at the Advanced Light Source (ALS) for optimal tuning of mechanically bendable x-ray mirrors for diffraction-limited soft x-ray nano-focusing. For ex situ tuning of the benders for optimal beam-line performance, we use a revised version of the method of characteristic functions recently developed at the ALS optical metrology laboratory. At-wavelength optimal tuning of bendable optics consists of a series of wavefront-sensing tests with increasing accuracy and sensitivity, including modified scanning-slit Hartmann tests. The methods have been experimentally validated at ALS test beamline 5.3.1 and the micro-diffraction beamline 12.3.2 in applications to optimally set bendable Kirkpatrick-Baez mirrors designed for sub-micron focusing.

Methodology for optimalin situalignment and setting of bendable optics for nearly diffraction-limited focusing of soft x-rays

We demonstrate a comprehensive and broadly applicable methodology for the optimal in situ configuration of bendable soft x-ray Kirkpatrick-Baez mirrors. The mirrors used for this application are preset at the Advanced Light Source Optical Metrology Laboratory prior to beamline installation. The in situ methodology consists of a new technique for simultaneously setting the height and pitch angle of each mirror. The benders of both mirrors were then optimally tuned in order to minimize ray aberrations to a level below the diffraction-limited beam waist size of 200 nm (horizontal)×100 nm (vertical) . After applying this methodology, we measured a beam waist size of 290 nm (horizontal)×130 nm (vertical) with 1 nm light using the Foucault knife-edge test. We also discuss the utility of using a grating-based lateral shearing interferometer with quantitative wavefront feedback for further improvement of bendable optics.

Trends in X-ray Fluorescence Microscopy

Modern synchrotron-based X-ray fluorescence microscopy (XFM) has become a critical tool for many a research program, addressing extremely broad and highly relevant scientific questions. Their ability to map trace elemental content and probe local chemical state has been applied to numerous scientific areas in the life sciences [1–3], the environmental and earth sciences [4, 5], the materials sciences, as well as in cultural heritage studies. The newest generation of instruments utilizes high-brightness X-ray sources and incorporate state-of-the-art focusing optics and detector systems. Advances in X-ray sources and nanofocusing optics, for example, have allowed these instruments to achieve spatial resolutions of 20–30 nm using diffractive optics such as Fresnel zone plates and 200 nm using reflective optics such as Kirkpatrick-Baez mirrors. New beamlines, now in the design stage, aim to achieve similar (and better) resolutions within the next five years.

Split and Delay System for Soft X-ray Pump/Soft X-ray Probe Experiments at the LCLS Free Electron Laser

We will report on the development of a mirror based x-ray split and delay system for soft x-rays at the Linac Coherent Light Source free electron laser. The instrument will be based on an edge-polished mirror design, using grazing incidence mirrors to cover an energy range up 2000 eV. Two mirrors located immediately after the AMO Kirkpatrick-Baez mirrors will split the FEL wavefront; one of these mirrors will be translated and rotated to produce a variable delay up to 100 femtoseconds.

Plastic Deformation in Profile-Coated Elliptical KB Mirrors

Profile coating has been successfully applied to produce elliptical Kirkpatrick-Baez (KB) mirrors using both cylindrical and flat Si substrates. Previously, focusing widths of 70 nm with 15-keV monochromatic and 80 nm with white beam were achieved using a flat Si substrate. Now, precision elliptical KB mirrors with sub-nm figure errors are produced with both Au and Pt coatings on flat substrates. Recent studies of bare Si-, Au-, and Pt-coated KB mirrors under prolonged synchrotron X-ray radiation and low-temperature vacuum annealing will be discussed in terms of film stress relaxation and Si plastic deformation.

Sub-micrometre holotomographic characterisation of the effects of solution heat treatment on an AlMg7.3Si3.5 alloy

A strip cast AlMg7.3Si3.5 alloy is investigated by sub-micrometre holotomographic analysis achieving a voxel size of (60nm)3 by cone beam magnification of the focused synchrotron beam using Kirkpatrick-Baez mirrors. The three-dimensional microstructure of the same specimen volume in the as-cast state is compared with that after exposure to 540°C for 30min resolving microstructural features down to 180nm. The three-dimensional analysis of the architecture of the eutectic Mg2Si and the Fe-aluminides reveals how the as-cast microstructure changes during the solution treatment. The alloy in the as-cast condition contains a highly interconnected seaweed-like Mg2Si eutectic. The level of three-dimensional interconnectivity of the Mg2Si eutectic phase decreases by only partial disintegration during the heat treatment correcting the two-dimensional metallographic impression of isolated round particles. Statistical analyses of the particle distribution, sphericity, mean curvatures and Gaussian curvatures describe quantitatively the architectural changes of the Mg2Si phase. This explains the decrease of the high temperature strength of the alloy by the solution treatment tested in hot compression.

A combined Kirkpatrick-Baez mirror and multilayer lens for sub-10 nm x-ray focusing

We have used a combined optical system of a high gain elliptic Kirkpatrick-Baez mirror system (KB) and a multilayer Laue lens (MLL) positioned in the focal plane of the KB for hard x-rays nano-focusing. The two-step focusing scheme is based on a high acceptance and high gain elliptical mirror with moderate focal length and a MLL with ultra-short focal length. Importantly, fabrication constraints, i.e. in mirror polishing and bending, as well as MLL deposition can be significantly relaxed, since (a) the mirror focus in the range of 200-500 nm is sufficient, and (b) the number of layers of the MLL can be correspondingly small. First demonstrations of this setup at the coherence beamline of the PETRA III storage ring yield a highly divergent far-field diffraction pattern, from which the autocorrelation function of the near-field intensity distribution was obtained. The results show that the approach is well suited to reach smallest spot sizes in the sub-10nm range at high flux.

Ultra-precise characterization of LCLS hard X-ray focusing mirrors by high resolution slope measuring deflectometry

We present recent results on the inspection of a first diffraction-limited hard X-ray Kirkpatrick-Baez (KB) mirror pair for the Coherent X-ray Imaging (CXI) instrument at the Linac Coherent Light Source (LCLS). The full KB system - mirrors and holders - was under inspection by use of high resolution slope measuring deflectometry. The tests confirmed that KB mirrors of 350mm aperture length characterized by an outstanding residual figure error of <1 nm rms has been realized. This corresponds to the residual figure slope error of about 0.05µrad rms, unprecedented on such long elliptical mirrors. Additional measurements show the clamping of the mirrors to be a critical step for the final - shape preserving installation of such outstanding optics.

Single-nanometer focusing of hard x-rays by Kirkpatrick–Baez mirrors

We have constructed an extremely precise optical system for hard-x-ray nanofocusing in asynchrotron radiation beamline. Precision multilayer mirrors were fabricated, tested, andemployed as Kirkpatrick–Baez mirrors with a novel phase error compensator. In the phasecompensator, an at-wavelength wavefront error sensing method based on x-rayinterferometry and an in situ phase compensator mirror, which adaptively deforms withnanometer precision, were developed to satisfy the Rayleigh criterion to achievediffraction-limited focusing in a single-nanometer range. The performance of the optics wastested at BL29XUL of SPring-8 and was confirmed to realize a spot size of approximately7 nm.

Achromatic nested Kirkpatrick–Baez mirror optics for hard X-ray nanofocusing

The first test of nanoscale-focusing Kirkpatrick-Baez (KB) mirrors in the nested (or Montel) configuration used at a hard X-ray synchrotron beamline is reported. The two mirrors are both 40 mm long and coated with Pt to produce a focal length of 60 mm at 3 mrad incident angle, and collect up to a 120 µm by 120 µm incident X-ray beam with maximum angular acceptance of 2 mrad and a broad bandwidth of energies up to 30 keV. In an initial test a focal spot of about 150 nm in both horizontal and vertical directions was achieved with either polychromatic or monochromatic beam. The nested mirror geometry, with two mirrors mounted side-by-side and perpendicular to each other, is significantly more compact and provides higher demagnification than the traditional sequential KB mirror arrangement. Ultimately, nested mirrors can focus larger divergence to improve the diffraction limit of achromatic optics. A major challenge with the fabrication of the required mirrors is the need for near-perfect mirror surfaces near the edge of at least one of the mirrors. Special polishing procedures and surface profile coating were used to preserve the mirror surface quality at the reflecting edge. Further developments aimed at achieving diffraction-limited focusing below 50 nm are underway.

BioCARS: a synchrotron resource for time-resolved X-ray science

BioCARS, a NIH-supported national user facility for macromolecular time-resolved X-ray crystallography at the Advanced Photon Source (APS), has recently completed commissioning of an upgraded undulator-based beamline optimized for single-shot laser-pump X-ray-probe measurements with time resolution as short as 100 ps. The source consists of two in-line undulators with periods of 23 and 27 mm that together provide high-flux pink-beam capability at 12 keV as well as first-harmonic coverage from 6.8 to 19 keV. A high-heat-load chopper reduces the average power load on downstream components, thereby preserving the surface figure of a Kirkpatrick-Baez mirror system capable of focusing the X-ray beam to a spot size of 90 µm horizontal by 20 µm vertical. A high-speed chopper isolates single X-ray pulses at 1 kHz in both hybrid and 24-bunch modes of the APS storage ring. In hybrid mode each isolated X-ray pulse delivers up to ~4 × 10(10) photons to the sample, thereby achieving a time-averaged flux approaching that of fourth-generation X-FEL sources. A new high-power picosecond laser system delivers pulses tunable over the wavelength range 450-2000 nm. These pulses are synchronized to the storage-ring RF clock with long-term stability better than 10 ps RMS. Monochromatic experimental capability with Biosafety Level 3 certification has been retained.

Element-specific high-resolution diffraction microscopy using focused hard X-ray beam

We demonstrated high-resolution element-specific diffraction microscopy using a hard X-ray beam focused by Kirkpatrick–Baez mirrors. Coherent diffraction patterns of an Au/Ag nanoparticle were measured at incident X-ray energies around the Au LIII absorption edge. By calculating the difference between the intensities of reconstructed images obtained at different energies, an image of the Au element could be derived. From the difference image, it was suggested that the replacement reaction progresses from the corners of Ag cubic particle.

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 1nm is required in the useable area along the X-ray footprint with a ∼0.1mm-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.

The sub-micron resolution X-ray spectroscopy beamline at NSLS-II

Abstract For many research areas such as life, environmental, earth or material sciences, novel analytical resources have to be developed for an advance understanding of complex natural and engineered systems that are heterogeneous on the micron to the tenths of microns scale. NSLS-II at BNL will be a synchrotron radiation source with an ultra-high brilliance delivering a high current (500 mA). One of the 1st six NSLS-II beamlines will be the Sub-micron Resolution X-ray spectroscopy beamline (SRX), dedicated as an analytical tool to study complex systems on a sub-micron length scale. SRX will comprise two branches thanks to a canted setup with two undulators: the first branch using Kirkpatrick–Baez mirrors as focusing optics will cover the energy range of 4.65–23 keV, allowing for XANES experiments from the Ti to the Rh K-edge. Thanks to a horizontally deflecting double crystal monochromator with maximum stability, a set of slits located on the secondary source, and two sets of complementary and quickly interchangeable KB mirrors, spectroscopy with very high spectral and spatial resolution will be achieved. The spot size will almost fully cover a range from 60×60 to 1300×500 nm2, providing an attractive adaptability of the observation scale. A 1.5 m long IVU21 will serve as a light source. The expected high flux in a sub-micron-spot (5×1012 and 7×1013 ph s−1 at maximum and lowest resolutions) will open new possibilities for spectromicroscopy of trace elements. The 2nd canted undulator will serve as an independent light source for the second branch designed for experiments with X-ray energies in the range of 2–15 keV. Using Fresnel zone plates, the spatial resolution aimed for is around 30 nm with up to 7×109 ph s−1 in the spot. This branch would be attractive for many biological applications from life and environmental science due to low-Z elements of interest within that energy range. In both experimental stations, X-ray fluorescence will be used for imaging, spectroscopy, tomography and μ-diffraction experiments.

Hard X-ray nano-focusing with Montel mirror optics

Kirkpatrick–Baez mirrors in the Montel (or nested) configuration were tested for hard X-ray nanoscale focusing at a third generation synchrotron beamline. In this scheme, two mirrors, mounted side-by-side and perpendicular to each other, provide for a more compact focusing system and a much higher demagnification and flux than the traditional sequential K–B mirror arrangement. They can accept up to a 120 μm×120 μm incident X-ray beam with a long working distance of 40 mm and broad-bandpass of energies up to ∼30 keV. Initial test demonstrated a focal spot of about 150 nm in both horizontal and vertical directions with either polychromatic or monochromatic beam. Montel mirror optics is important and very appealing for achromatic X-ray nanoscale focusing in conventional non-extra-long synchrotron beamlines.

Improved focusing capability for inelastic X-ray spectrometer at 3-ID of the APS: A combination of toroidal and Kirkpatrick-Baez (KB) mirrors

Abstract We have combined a toroidal and a KB mirror system in tandem to improve the focal spot size for the momentum-resolved inelastic X-ray scattering (IXS) spectrometer at Sector 3 in APS. This combination provides a factor of 40 gain in flux density and 20 μm (H)×17 μm (V) (FWHM) in beam size at the sample position, enhancing the capability of the beamline for high-pressure measurements.

Optics upgrades at the APS beamline 20-BM

Recently, beamline 20-BM has been upgraded with new optics. A large bent cylindrical focusing mirror has been installed to provide an intense focused beam. It is designed to operate over the energy range 2.7–30 keV, and features a novel Al 2 O 3 /Pt coating. When operated near 2.6 mrad, the Pt coating provides good reflectivity up to 30 keV. The Al 2 O 3 overlayer minimizes the influence of the Pt M and L edges. The second upgrade that is in progress is the development of longer KB mirrors. A prototype bender has achieved a focus of about 2.5 μm using a 300 mm long mirror. Analysis of the focal spot indicates that the size is dominated by the slope errors of the mirror, and can be further reduced if these are minimized by better mirrors or by using differential coating methods.