The Nuclear Spectroscopic Telescope ARray (NuSTAR) is a NASA Small Explorer mission that will carry the first focusing hard X-ray (5–80 keV) telescope to orbit. The ground calibration of the optics posed a challenge as the need to suppress finite source distance effects over the full optic and the energy range of interest were unique requirements not met by any existing facility. In this paper we present the requirements for the NuSTAR optics ground calibration, and how the Rainwater Memorial Calibration Facility, RaMCaF, is designed to meet the calibration requirements. The nearly 175 m long beamline sports a 48 cm diameter 5–100 keV X-ray beam and is capable of carrying out detailed studies of large diameter optic elements, such as the NuSTAR optics, as well as flat multilayer-coated Silicon wafers.
This paper describes the design, crystal selection, and crystal testing for a vertical Johann spectrometer operating in the 13 keV range to measure ion Doppler broadening in inertial confinement plasmas. The spectrometer is designed to use thin, curved, mica crystals to achieve a resolving power of E/ Δ E > 2000. A number of natural mica crystals were screened for flatness and X-ray diffraction width to find samples of sufficient perfection for use in the instrument. Procedures to select and mount high quality mica samples are discussed. A diode-type X-ray source coupled to a dual goniometer arrangement was used to measure the crystal reflectivity curve. A procedure was developed for evaluating the goniometer performance using a set of diffraction grade Si crystals. This goniometer system was invaluable for identifying the best original crystals for further use and developing the techniques to select satisfactory curved crystals for the spectrometer.
We present an overview on the EUV/XUV activities of the Laser-Laboratorium Göttingen based on table-top laser-produced plasma (LPP) sources. As target materials, gaseous jets of noble gases or solid Gold are employed. In order to obtain high EUV fluence, a Schwarzschild objective consisting of two spherical mirrors with Mo/Si multilayer coatings is adapted to the source. By demagnified (10x) imaging of the Au plasma, an EUV spot with a maximum energy density of ~ 1.3 J/cm 2 is generated (3 μ m diameter, pulse duration 8.8 ns). First applications of this system reveal its potential for high-resolution modification and direct structuring of solid surfaces. Additionally, an EUV/XUV setup for structural analysis was developed. Using a gas puff target combined with a grazing incidence optics (Kirkpatrick-Baez arrangement), it offers the possibility to perform angular resolved reflectivity, diffraction, and scattering experiments. For chemical analysis of various samples, an NEXAFS setup was built, based on gaseous Krypton as a broadband emitter in the water-window range around the carbon K-edge (4.4 nm). Here, proof-of-principle for NEXAFS with lab-scaled XUV sources is given on polyimide as a reference.
The UK Smart X-Ray Optics (SXO) programme is developing active/adaptive optics for terrestrial applications. One of the technologies proposed is microstructured optical arrays (MOAs), which focus X-rays using grazing incidence reflection through consecutive aligned arrays of microscopic channels. Although such arrays are similar in concept to polycapillary and microchannel plate optics, they can be bent and adjusted using piezoelectric actuators providing control over the focusing and inherent aberrations. Custom configurations can be designed, using ray tracing and finite element analysis, for applications from sub-keV to several-keV X-rays, and the channels of appropriate aspect ratios can be made using deep silicon etching. An exemplar application will be in the microprobing of biological cells and tissue samples using Ti Kα radiation (4.5 keV) in studies related to radiation-induced cancers. This paper discusses the optical design, modelling, and manufacture of such optics.
An overview is given of the study on X-ray focusing using the Fabry-Perot type multi-plate silicon crystal cavities consisting of compound refractive lenses. Silicon (12 4 0) is used as the back reflection for cavity resonance at the photon energy of 14.4388 keV. Measurements of focal length of the transmitted beam through the crystal cavities show enhanced focusing effect due to the presence of back diffraction. Also, an incident beam with ultrahigh energy resolution can improve the focusing owing to the wider acceptance angle of the back diffraction. Considerations based on the excitation of dispersion surface within the framework of X-ray dynamical diffraction theory are also presented to reveal the origin of this enhanced focusing.
We present details of design of elliptically bent Kirkpatrick-Baez mirrors developed and successfully used at the advanced light source for submicron focusing. A distinctive feature of the mirror design is an active temperature stabilization based on a Peltier element attached directly to the mirror body. The design and materials have been carefully optimized to provide high heat conductance between the mirror body and substrate. We describe the experimental procedures used when assembling and precisely shaping the mirrors, with special attention paid to laboratory testing of the mirror-temperature stabilization. For this purpose, the temperature dependence of the surface slope profile of a specially fabricated test mirror placed inside a temperature-controlled container was measured. We demonstrate that with active mirror-temperature stabilization, a change of the surrounding temperature by more than 3 K does not noticeably affect the mirror figure. Without temperature stabilization, the rms slope error is changed by approximately 1.5 μrad (primarily defocus) under the same conditions.
We review feasibility studies, technological developments, and the astrophysical prospects for Laue lenses devoted to hard X-/gamma-ray astronomy observations.
Total-external-reflection Kirkpatrick-Baez mirror optics for high-energy X-rays have been applied to the X-ray microprobe at beamline 37XU of SPring-8. A focused beam size of 1.0 μm (V)×0.83 μm (H) has been achieved at an X-ray energy of 30 keV, and a total photon flux of the focused beam was about 5×109 photons/s. Micro-X-ray fluorescence (μ-XRF) analysis of the uranium distribution in rat kidneys has been performed with the mirror-focused beam. The sensitivity of uranium was evaluated from the XRF intensity of thin standard samples, and the minimum detection limit was estimated at 10 μg/g. The high-spatial-resolution analysis revealed that uranium was concentrated in the epithelium of the proximal tubules in the inner cortex. The maximum concentration of uranium in the tubule was estimated to be 503 μg/g using a semiquantitative evaluation.
A Fresnel zone plate (FZP) with 35 nm outermost zone width has been fabricated and tested in the hard X-ray region. The FZP was made by electron beam lithography and reactive ion etching technique. The performance test of the FZP was carried out by measuring the focused beam profile for coherent hard X-ray beam at the beamline 20XU of SPring-8. The full width at half maximum of the focused beam profile measured by knife-edge scan method is 34.9±2.7 nm, that agrees well with the theoretical value of diffraction-limited resolution. Applications to scanning microscopy were also carried out.
Thin foil mirrors were introduced as a means of achieving high throughput in an X-ray astronomical imaging system in applications for which high angular resolution was not necessary. Since their introduction, their high filling factor, modest mass, relative ease of construction, and modest cost have led to their use in numerous X-ray observatories, including the Broad Band X-ray Telescope, ASCA, and Suzaku. The introduction of key innovations, including epoxy replicated surfaces, multilayer coatings, and glass mirror substrates, has led to performance improvements and in their becoming widely used for X-ray astronomical imaging at energies above 10 keV. The use of glass substrates has also led to substantial improvement in angular resolution and thus their incorporation into the NASA concept for the International X-ray Observatory with a planned 3 m diameter aperture. This paper traces the development of foil mirrors from their inception in the 1970s through their current and anticipated future applications.
We have developed a new CCD-based radiographic camera called CrystalEyeCam for use in shock physics experiments: it is composed of two turning mirrors and an objective to relay the (visible) image from a scintillator assembly to a highly sensitive, low noise CCD camera. The objective was specifically developed to match our needs and has few chromatic and geometric aberrations and high photometric performance. The scintillator assembly is constructed using a specific (patented) technique of assembling monolithic scintillating crystals. It replaces the segmented scintillator previously used at our facility and produces higher quality images (better resolution and no segmentation). The sensitivity, noise level, detection threshold and resolution of CrystalEyeCam were measured using an 18-MeV-bremsstrahlung spectrum, filtered with 10 cm of lead, and two BGO assemblies: 20 and 30 mm in thickness, respectively. In particular, with the 30 mm-thick BGO assembly, the measured detection threshold of the imager (at ) is 1 μGy(air) and its resolution is ~1 mm. For 4-MeV incident photons, the estimated (energy) stopping power of the scintillator is 41%. The scintillator assembly thus proved to be a cheaper, effective alternative to segmented scintillators for use in CrystalEyeCam.
The multilayer Laue lens (MLL) is a novel diffractive optic for hard X-ray nanofocusing, which is fabricated by thin film deposition techniques and takes advantage of the dynamical diffraction effect to achieve a high numerical aperture and efficiency. It overcomes two difficulties encountered in diffractive optics fabrication for focusing hard X-rays: (1) small outmost zone width and (2) high aspect ratio. Here, we will give a review on types, modeling approaches, properties, fabrication, and characterization methods of MLL optics. We show that a full-wave dynamical diffraction theory has been developed to describe the dynamical diffraction property of the MLL and has been employed to design the optimal shapes for nanofocusing. We also show a 16 nm line focus obtained by a partial MLL and several characterization methods. Experimental results show a good agreement with the theoretical calculations. With the continuing development of MLL optics, we believe that an MLL-based hard x-ray microscope with true nanometer resolution is on the horizon.
The successful commissioning of the XMM-Newton focal plane detectors, radiation hard X-ray imaging spectroscopic CCDs, has attracted some attention: Reliably operating X-ray CCDs are delivering extraordinary images, recorded in a single-photon counting mode, imaged through the largest X-ray telescope ever built. The experimental boundary conditions from space applications will serve as a setting to confine the scope of this review. Of course, related applications in other fields of basic and applied science will also be treated. State of the art X-ray detectors with energy, position and time resolution at high quantum efficiency from the near-infrared up to 20 keV are described in detail: todays most advanced systems comprise charge coupled devices and active pixel sensors as well as pixellized silicon drift detectors. They have been developed for astrophysics experiments in space, for material analysis and for experiments at synchrotron radiation facilities. The functional principles of the silicon devices are derived from basic solid-state device physics. The spatial resolution, the spectroscopic performance of the systems, the long-term stability and the limitations of the detectors are described in detail. Field applications show the unique usefullness of silicon radiation detectors.
This paper provides a comprehensive overview on the utilization of curved graded multilayer coatings as focusing elements for hard X-rays. It concentrates on the Kirkpatrick-Baez (KB) focusing setup that has been developed at 3rd generation synchrotron sources worldwide. The optical performance of these devices is evaluated applying analytical and numerical approaches. The essential role of the multilayer coating and its meridional d-spacing gradient are discussed as well as important technological issues. Experimental data and examples of operational KB focusing devices and applications complement the work.
Diffractive X-ray telescopes using zone plates, phase Fresnel lenses, or related optical elements have the potential to provide astronomers with true imaging capability with resolution several orders of magnitude better than available in any other waveband. Lenses that would be relatively easy to fabricate could have an angular resolution of the order of microarcseconds or even better, that would allow, for example, imaging of the distorted spacetime in the immediate vicinity of the supermassive black holes in the center of active galaxies What then is precluding their immediate adoption? Extremely long focal lengths, very limited bandwidth, and difficulty stabilizing the image are the main problems. The history and status of the development of such lenses is reviewed here and the prospects for managing the challenges that they present are discussed.
This Special Issue of X-Ray Optics and Instrumentation comprises ten review papers and six research articles, which collectively offer a broad overview of X-ray focusing techniques and applications in laboratory measurements, in synchrotron beamlines, and in X-ray astronomy.Focusing enables not only more intense illumination for reduced exposure time and higher signal-to-noise ratio, but higher spatial resolution through true imaging.Although X-ray focusing is accomplished through the application of some basic physical principles, such as reflection (mirrors), refraction (lenses), and diffraction (crystals or zone plates), stringent performance requirements coupled with physical, mechanical, environmental, and manufacturability imperatives or limitations make the task technically challenging.The diverse X-ray focusing techniques and applications covered in this Volume provide a glimpse into the scope, challenges, and future of this expanding field.
In recent years, technological developments in the area of extreme ultraviolet lithography (EUVL) have experienced great improvements. So far, intense light sources based on discharge or laser plasmas, beam steering and imaging optics as well as sensitive detectors are available. Currently, applications of EUV radiation apart from microlithography, such as metrology, high-resolution microscopy, or surface analysis come more and more into focus. In this contribution we present an overview on the EUV/XUV activities of the Laser-Laboratorium Göttingen based on table-top laser-produced plasma (LPP) sources. As target materials gaseous or liquid jets of noble gases or solid Gold are employed. Depending on the applications, the very clean but low intense gaseous targets are mainly used for metrology, whereas the targets for high brilliances (liquid, solid) are used for microscopy and direct structuring. For the determination of interaction mechanisms between EUV radiation and matter, currently the solid Gold target is used. In order to obtain a small focal spot resulting in high EUV fluence, a modified Schwarzschild objective consisting of two spherical mirrors with Mo/Si multilayer coatings is adapted to this source. By demagnified (10x) imaging of the Au plasma an EUV spot of 3 μm diameter with a maximum energy density of ~1.3 J/cm2 is generated (pulse duration 8.8 ns). First applications of this integrated source and optics system reveal its potential for high-resolution modification and direct structuring of solid surfaces. For chemical analysis of various samples a NEXAFS setup was developed. It consists of a LPP, using gaseous Krypton as a broadband emitter in the water-window range, as well as a flat field spectrograph. The laboratory system is set to the XUV spectral range around the carbon K-edge (4.4 nm). The table-top setup allows measurements with spectral accuracy comparable to synchrotron experiments. NEXAFS-experiments in transmission and reflection are demonstrated. Beside chemical investigations, also microscopy applications are performed within the XUV spectral range. For this reason a water-window microscope was developed, based on a liquid argon LPP target. The XUV radiation is focused by a Cr/Sc multilayer mirror, leading to spectral narrow band radiation on the sample. For magnifying the sample, a Fresnel zone plate will be used with an outer zone width of 50 nm. Additionally to these applications, an EUV/XUV setup for structural analysis was developed. Using a spectral broad band emitting Xenon gaseous target combined with a grazing incidence optics (Kirkpatrick-Baez arrangement), it offers the possibility to perform angular resolved reflectivity-, diffraction- and scattering experiments as well as NEXAFS analysis in one setup. In completion to these experiments with LPP sources, an EUV/XUV Hartmann-type wavefront sensor has been developed in collaboration with DESY HASYLAB. It consists of a pinhole array, positioned in front of a XUV sensitive CCD camera with quantum converter. With custom-developed software the incident wavefront can be determined. This sensor is currently used at the free electron laser FLASH in Hamburg for beam characterization.
Silicon Pore Optics (SPO) is a new X-ray optics technology under development in Europe, forming the ESA baseline technology for the International X-ray Observatory candidate mission studied jointly by ESA, NASA, and JAXA. With its matrix-like structure, made of monocrystalline-bonded Silicon mirrors, it can achieve the required angular resolution and low mass density required for future large X-ray observatories. Glass-based Micro Pore Optics (MPO) achieve modest angular resolution compared to SPO, but are even lighter and have achieved sufficient maturity level to be accepted as the X-ray optic technology for instruments on board the Bepi-Colombo mission, due to visit the planet Mercury. Opportunities for technology transfer to ground-based applications include material science, security and scanning equipment, and medical diagnostics. Pore X-ray optics combine high performance with modularity and economic industrial production processes, ensuring cost effective implementation.
Focusing X-ray telescopes have been the most important factor in X-ray astronomy’s ascent to equality with optical and radio astronomy. They are the prime tool for studying thermal emission from very high temperature regions, non-thermal synchrotron radiation from very high energy particles in magnetic fields and inverse Compton scattering of lower energy photons into the X-ray band. Four missions with focusing grazing incidence X-ray telescopes based upon the Wolter 1 geometry are currently operating in space within the 0.2 to 10 keV band. Two observatory class missions have been operating since 1999 with both imaging capability and high resolution dispersive spectrometers. They are NASA’s Chandra X-ray Observatory, which has an angular resolution of 0.5 arc seconds and an area of 0.1 m 2 and ESA’s XMM-Newton which has 3 co-aligned telescopes with a combined effective area of 0.43 m 2 and a resolution of 15 arc seconds. The two others are Japan’s Suzaku with lower spatial resolution and non-dispersive spectroscopy and the XRT of Swift which observes and precisely positions the X-ray afterglows of gamma-ray bursts. New missions include focusing telescopes with much broader bandwidth and telescopes that will perform a new sky survey. NASA, ESA, and Japan’s space agency are collaborating in developing an observatory with very large effective area for very high energy resolution dispersive and non-dispersive spectroscopy. New technologies are required to improve upon the angular resolution of Chandra. Adaptive optics should provide modest improvement. However, orders of magnitude improvement can be achieved only by employing physical optics. Transmitting diffractive-refractive lenses are capable theoretically of achieving sub-milli arc second resolution. X-ray interferometry could in theory achieve 0.1 micro arc second resolution, which is sufficient to image the event horizon of super massive black holes at the center of nearby active galaxies. However, the physical optics systems have focal lengths in the range 10 3 to 10 4 km and cannot be realized until the technology for accurately positioned long distance formation flying between optics and detector is developed.
A summary of focusing X ray polycapillary optics is presented including history, theory, modeling, and applications development. The focusing effects of polycapillary optics come from the overlap of the beams from thousands of small hollow glass tubes. Modeling efforts accurately describe optics performance to allow for system development in a wide variety of geometries. The focusing of X ray beams with polycapillary optics yields high gains in intensity and increased spatial resolution for a variety of clinical, lab-based, synchrotron or in situ analysis applications.
