A one-kilometer long synchrotron radiation beamline with an x- ray undulator source was completed at SPring-8. The beamline was planned to facilitate various applications of a wide-area coherent x-ray beam, development of bi-crystal x-ray interferometers for gravitational red-shift measurement and development of highly sensitive diagnostic methods of accelerator dynamics. This paper reports the structure of the long beamline as well as some selected first results including phase contrast imaging and diffraction imaging applications.
The optics at the F2 station of CHESS have been completely redesigned and rebuilt. The new design consists of a white- beam collimating mirror and a fixed-exit double-crystal monochromator, which are optimized for the growing field of multiple-wavelength anomalous diffraction (MAD) crystallography. The upstream mirror reduces the heat load onto the monochromator by two-thirds and increases the energy resolution of the x-ray beam to its source-size limit. The new single-rotation fixed-exit monochromator employs a slightly- tilted second-crystal translation that allows fast and reliable changes in the energy of the outgoing beam while maintaining its beam position. Two additional angle-segment stages, one for each crystal, are used to fine tune the second-crystal translation tilt so that the translation stage can be always positioned along the tangent of the desired loci of the second crystal for a wide energy range of 7 - 17 keV using Si (111).
With the development of high quality x-ray mirrors and x-ray zone plates, the use of micron-size x-ray beams is growing rapidly. The size of the focal spot is frequently characterized by measuring either the transmitted or fluorescence counting rate as a knife edge is scanned through the beam; the full width half maximum (FWHM) of the derivative of this scan is often quoted as the 'resolution' of the system. Many systems have been built which are claimed to have a focal spot size of 1 micrometer2 or less. Unfortunately, this parameter does not give an accurate presentation of the focal quality of the beam. We have developed a test using a pattern of microfabricated 'dots' on a silicon wafer to measure the encircled energy in an x-ray focal spot as a function of radius. Using this test, we have found that focused x-ray beams frequently have a large, low intensity flare that is not represented in the beam profile as measured by the knife edge scan method. This flare can be produced by several factors including diffuse scattering from the mirror surfaces and higher orders of a zone plate. It can cause serious errors in when calculating elemental concentrations in heterogeneous samples. In addition, for micro-XAS experiments where the energy is scanned to identify the compound at a particular point, this flare may vary as a function of energy and therefore change the XAS spectra from a small particle in a complex sample.
A double crystal, multilayer monochromator was designed and fabricated for a wiggler beamline at the Cornell High Energy Synchrotron Source (CHESS). The monochromator consists of an internally water-cooled first substrate and a fixed-radius sagittally focusing second substrate, each coated with a multilayer consisting of 100 bilayers of Tungsten/Carbon with a 27 angstrom d-spacing. The wide energy bandpass of this multilayer along with sagittal focusing provides the best available flux for time resolved experiments. A flux 100 times that of conventional silicon monochromators is possible and allows for a finer time resolution for the crystal growth studies on this beamline. For other experimental uses, the higher intensity allows for more rapid data collection.
The x-ray telescopes foreseen for future x-ray missions will need an high number of mirrors. Using for their production the replication method, an high number of mandrels will be necessary. A cost-effective approach that offers accurate control of the mandrels shape is the ion beam figuring. Using this procedure the aluminum-kanigen mandrels are initially optically figured by diamond turning or by other means, superpolished to the specified microroughness and then ion beam figured to the required shape. An ion beam facility has been built to test the concept. A small test mandrel has been measured obtaining the map of its surface. From this map and from the beam removal function of the ion head a time matrix has been computed to remove the shape errors. Using this time matrix as input to the program that control the movement of the ion head, the mandrel has been corrected from the errors. In this paper is given a description of the ion beam facility and the results obtained figuring the surface of the test mandrel.
A grinding technique referred to as the McCarter Superfinish, for grinding large-size optical components is discussed and certain surface characterization information about flatness and the relative magnitude of the subsurface damage in silicon substrates is reported. The flatness measurements were obtained with a Wyko surface analyzer, and the substrate damage measurements were made by x-ray diffraction and acid etching. Results indicate excellent control of flatness and fine surface finish. X-ray measurements show that the diamond wheels with small particle sizes used in the final phases of the grinding operation renders surfaces with relatively small subsurface damage.
With the advent of third generation synchrotron radiation sources, more flux was available for the experimentalist. At the same time, the request in term of spot dimension and energy resolution rapidly increased. For this reason, opticians try to design beamlines with higher and higher performances. To this end the shape of every optical component of a beamline is specified to have very tight constrains, because every small figure error produces a sudden reduction in terms of the overall performance. Nevertheless, the necessity to positioning and cooling the components implies the presence of a safe clamping system which unavoidably would modifies the shape of the component, causing possible reduction of resolving power or increasing the spot dimension. Thus it is not sufficient to measure accurately the slope or the profile of a mirror in laboratory before the mounting, but it is useful to test it also after this procedure. We, at ELETTRA, have measured by means of a modified version of the LTP II (Long Trace Profiler) several mirrors and gratings before and after their clamping, in order to estimate the effect of the holder on the final performances of the beamlines. Since our LTP II measures directly the local slope of the surface under test with a repeatability better than 0.02 arcsec on a 1 meter long optical surface, it is very easy to single out any small distortion of the tangential profile introduced by the mounting system. Different kinds of supports for both small and large optical elements, were taken into consideration and the effect of the deformation induced by them on the beamline performance was simulated and will be presented here together with the results of each measurements. The results give us a way to select properly the kind of clamping and invite the opticians to try to take into consideration also this effect before designing a complex beamline.
We measured Pt/C multilayers and supermirrors with hard X-rays at synchrotron radiation facility SPring-8. These mirrors were fabricated for the hard X-ray telescope on board our balloon- borne experiment named InFOC(mu) S. The energy band of InFOC(mu) S telescope is from 20 to 40 keV, thus characterization of reflectors with hard X-rays above 20 keV is important. SPring-8 is one of the world's most powerful third-generation synchrotron radiation facility. We measured multilayers and several types of supermirrors. We also measured reflectivity of supermirrors on three different kind of substrates; float grass, gold replica foil and platinum replica foil. From the reflectivity measurements, performance of these supermirrors was found quite satisfactory for our telescope. Furthermore platinum replica foil substrate showed significantly better reflectivity than gold replica foil. Thus we chose platinum replica foil as a substrate for flight reflectors. Scattering measurements gave us important informations. Our preliminary analysis showed that the scattered power distribution can be explained as a convolution of structures in lateral and depth direction.
Presently there is a gap in energy resolution (Delta) E/E between a few percent for multilayer x-ray optics and a few 10-4 for perfect crystal optics. One approach to bridge this gap is the development of high-resolution multilayers. We will report on recent advances in this field and discuss both the capabilities and the limitations of this solution. The deposition of hundreds of layers of hard materials is a considerable challenge for the coating system, and stability issues have to be considered with particular care. We have shown theoretically and experimentally that this challenge can be met with a combination of Al2O3 and B4C. With 680 bilayers we reached a spectral resolution < 0.3% and a peak reflectivity of almost 50% for 12 keV x- rays. The disagreement with the diffraction properties of a perfect multilayer system could be accurately described by instabilities during the deposition process. With improved stability, such systems can provide still better performances.
Multilayer structures with depth-graded spacing can show a high reflectivity in a broad energy passband for hard X-rays if the interface roughness/diffuseness is controlled and minimized. We present a study of several multilayer systems deposited by DC magnetron sputtering on <111> silicon wafers and superpolished fused silica substrates. The material combinations discussed are W/Si, WSi2/Si, W/C, Pt/C, Ni/C, Ni/B4C, and Mo/Si. The deposition method used was DC magnetron sputtering at low argon pressures (1.5 to 5 mT). The characterization methods used were: Atomic Force Microscopy in tapping mode, stylus profilometry, Rutherford backscattering, cross sectional TEM, and specular X-ray reflectivity (XRR) scans at 8.05 keV. Different process parameters were varied in order to optimize the interface roughness/diffuseness (sigma) that was measured by XRR scans.
We present the results of theoretical calculations pertaining to the control of the film thickness distribution in two dimensions. The calculations are relevant to magnetron sputter deposition in which two different deposition geometries are considered. One of which is for an 'in-line' system where the substrate passes along a linear path in front of each target, and the other for cylindrical deposition geometry where the substrates are mounted on a rotating drum. Results of various thickness gradients on flat as well as spherical and cylindrical substrates are shown. The thickness distribution in one dimension is controlled by the use of a contoured shield which appropriately intercepts sputtered material between the target and substrate. The film thickness in the other dimension is controlled by changing the velocity of the substrate through the deposition region. The shield contour and velocity profile required to achieve these gradients are also given.
The x-ray reflectivity of a multilayer is a non-linear function of many parameters (materials, layer thicknesses, densities, roughness). Non-linear fitting of experimental data with simulations requires to use initial values sufficiently close to the optimum value. This is a difficult task when the space topology of the variables is highly structured, as in our case. The application of global optimization methods to fit multilayer reflectivity data is presented. Genetic algorithms are stochastic methods based on the model of natural evolution: the improvement of a population along successive generations. A complete set of initial parameters constitutes an individual. The population is a collection of individuals. Each generation is built from the parent generation by applying some operators (e.g. selection, crossover, mutation) on the members of the parent generation. The pressure of selection drives the population to include 'good' individuals. For large number of generations, the best individuals will approximate the optimum parameters. Some results on fitting experimental hard x-ray reflectivity data for Ni/C multilayers recorded at the ESRF BM5 are presented. This method could be also applied to the help in the design of multilayers optimized for a target application, like for an astronomical grazing-incidence hard X-ray telescopes.
The optical configuration of the monochromator for the new beamline X-MOSS at the ELETTRA synchrotron ring is described. The requirements for this instrument are to collect a 3 mrad X 2 mrad aperture beam produced by a bending magnet in the 3 - 1400 eV energy range; the energy resolution has to be 3000 or better over the whole range, with a focused beam of the order of 10 - 50 micrometer. The designed monochromator, presently under construction, is a slitless four grazing incidence optical elements: the first element is a one-meter paraboloidal mirror in sagittal focusing, then there is a plane mirror-plane grating dispersion system and finally a second one-meter paraboloidal mirror, also used in sagittal focusing. The latter focuses the radiation on the monochromator exit slit. This monochromator design is not limited by a defined working curve: in this way it is possible to select the preferred operational parameters, to optimize either the flux or the resolution or the high order rejection. The monochromatic beam is finally sent on the sample under examination by an ellipsoidal refocusing mirror.
Some experiments performed at bending magnet beamlines at the Advanced Photon Source (APS) will benefit from a focused photon beam. A commercial sagittal focusing bender that uses a simple rectangular plate as the diffraction element could be utilized for this purpose. However, the thin rectangular diffracting plate, specified by the manufacturer, is susceptible to anticlastic bending. A simple ribbed plate that utilizes this commercial bender but that reduces anticlastic bending is proposed as a solution. This design uses a pair of sufficiently stiff ribs on the diffracting surface, which substantially suppresses anticlastic bending. The finite element analysis (FEA) method was used to predict the overall structural response of this sagittally bent plate and its anticlastic distortion. Results are compared with unribbed plates showing an effective reduction in anticlastic bending.
The first successful tests of a graded crystal x-ray monochromator at BESSY II based on SiGe crystals are reported. The monochromator crystals with Ge concentration gradient of 0.8%/cm along the crystal surface have been tested at the KMC- 2 beamline. The beam from the BESSY II bending magnet with vertical divergence of 0.2 mrad was used. In comparison with conventional Si crystals the enhancement of an energy resolution is 3 - 5 times and, simultaneously, increase of spectral flux density of 4 - 6 times were obtained.
Experimental observations of synchrotron radiation diffraction from a thin surface layer at a 90-degree Bragg reflection are reported and discussed. The synchrotron experiments were performed using a bending magnet source at the European Synchrotron Radiation Facility (ESRF) in France and undulator sources at the Advanced Photon Source (APS) in the U.S. and SPring-8 in Japan. Thin (0.5, 1.0 and 1.5 micron) InGaAs films deposited on a GaAs (100) substrate were studied near the 90- degree using the GaAs (800) reflection. A slight, less than 0.1%, difference in the lattice spacing between the layer and the substrate is sufficient to allow a direct and exclusive observation of the diffraction profile from a thin layer as if it was a 'free-standing' thin crystal. This research opens new possibilities for x-ray optical schemes and the development of novel analytical techniques for surface/interface x-ray diffraction studies.
This paper reports new techniques for hard x-ray modulation spectroscopy, helicity modulation and energy modulation, which have been developed at SPring-8. The helicity modulation technique has been realized by combination of fast helicity switching at 40 Hz using a transmission diamond x-ray phase retarder and a phase-sensitive (lock-in) detection system. Performance of the helicity modulation technique is demonstrated by measured spectra of x-ray magnetic circular dichroism of extremely high signal-to-noise ratio in the region near the Fe K-edge. A quick and precise method for the polarization tuning is presented, and the helicity modulation technique is shown to be applicable to magnetic EXAFS spectroscopies in wider energy region. For the energy modulation technique, fast energy switching has been made using a Si channel-cut crystal as a second monochromator of high energy resolution. An energy-derivative XAFS spectrum was directly obtained at the Mn K-edge, and illustrates the advantages of this technique in high energy resolution and noise reduction.
We present recent theoretical and instrumentation developments in phase-sensitive x-ray crystallography using a reference- beam data collection technique. The technique is based on the principle of three-beam or multiple-beam interference, but unlike the conventional method where interference profiles are measured one at a time, the reference-beam diffraction technique integrates three-beam diffraction into the popular oscillation method of data collection, and allows parallel recording of many three-beam interference profiles on an area detector simultaneously. Complete interference profiles are measured by taking multiple oscillation exposures while stepping through the rocking curve of the reference reflection. Recent developments include a portable five-circle kappa diffractometer designed to be a part of an automated reference-beam oscillation setup, and a simplified three-beam diffraction theory using a distorted-wave approach that can be used in reference-beam data analyses to extract the reflection phases.
Experimental observations of refraction/small angle scattering of synchrotron radiation from non-crystalline materials are reported and discussed. This technique constitutes a further application of an experimental-analytical x-ray phase retrieval technique previously utilized for Bragg diffraction data. The recent impetus for these studies arose from high resolution measurements of x-ray refraction phenomena from a narrow aperture performed in the laboratory, which suggested that the phase retrieval formalism could also be applied to non-crystalline materials. The experiments were performed using bending magnet sources at the European Synchrotron Radiation Facility (ESRF) in France, and the Photon Factory, Japan. Refraction/small-angle scattering data was collected from thin (20 - 125 micrometer) filaments of optical fiber (silica), copper, nylon6, kapton and human hair. The experimental results obtained are in close agreement with theoretical simulations. Successful application of the phase retrieval formalism to this data will establish a basis for a novel materials characterization technique.
Recent significant progress in development and construction of reflective X-ray optical elements (grazing incidence, multilayer and crystals) has been extremely fruitful. Current R&D activities for desired further developments and novel applications are hot. Higher collection efficiency of photons from laboratory X-ray sources, higher beam intensity, smaller focal spot, higher resolution and lower cost of X-ray optics still remain challenging. Higher level of technology and novel designs are the key issues. We discuss some possible new approaches and critical features of already known systems important for their optimization. Examples of computer ray tracing are shown for capillaries, ellipsoidal mirror and thin dense 2D Lobster-eye systems.
Conventional x-ray optics have low optical efficiency and wavelength dependent focusing. The use of grazing incidence reflective optics overcomes these problems and significant progress has been made using polycapillary systems based on commercial microchannel plates originally designed as electron multipliers. Microfabrication techniques, under development for microelectromechanical systems (MEMS), provide a means of making arrays of microchannels with radial symmetry for a wide range of x-ray optical applications. The focal length of such micro-optical arrays may be varied to provide a zoom lens capability.
Using the technology that has been developed over many years for the fabrication of glass micro-channel plates, a prototype micro-pore optic has been produced that is a very light and compact implementation of a Wolter-I optic for X-ray imaging. With this prototype true Wolter-I imaging has been observed for the first time in a micro-pore optic. Individual fibers in the plates are found to be quite good, with a surface roughness permitting application at medium X-ray energies. The image quality and effective area is however seriously reduced by random tilt errors of multifibers in the plates. If this limitation can be overcome, this technology would allow very light and compact X-ray telescopes to be built. A design is presented that already provides a considerable effective area for soft X-rays using the properties of the surfaces obtained in this program.
Planar x-ray waveguide structures can be used as resonant beam coupling devices to produce a coherent and divergent x-ray line source with cross-sections in the sub-micrometer range. This article reviews the basic x-ray optical properties of such devices and generalizes the principle of resonant x-ray beam coupling to waveguides containing multiple guiding layers. In such a device, several coherent beams of a width on the order of 100 angstrom to 1000 angstrom can be extracted at the end of the waveguide. Besides coherent diffraction and imaging, interferometry with two or more nanometer sized beams can be envisioned. Furthermore this article presents measurements of the internal reflection of an excited x-ray waveguide mode in a synthetic nanostructure defined by e-beam lithography. In this device the x-ray beam is first coupled into a conventional vertical thin film waveguide structure and then reflected laterally at the quasi one-dimensional edge of the waveguiding layer. The reflectivity of the quasi one- dimensional interface has been recorded under simultaneous excitation of the (vertical) waveguide mode. This experiment constitutes an important step towards the production of a coherent, nanometer sized x-ray point source by two- dimensionally defined waveguide structures.
We present the results of experiments with the concentrators based on the whispering-gallery effect and designed to transform a parallel x-ray beam into a converging one. A technology for manufacturing concentrators to focus parallel beams into small-sized spots is developed. The present status of the technology demonstrates the concentrators for the soft ((lambda) equals 44.6 angstrom) and intermediate ((lambda) equals 2 - 3 angstrom) x-ray bands. Using the UKROP facility, studies of the concentrator focusing properties were performed. For the soft x-ray radiation, the focal spot diameter was measured as 0.17 mm (FWHM), focal-spot-to- incident-beam intensity growth coefficient was evaluated as 180, and the radiation transmission efficiency was estimated as 8%. For the intermediate x-ray radiation, the focal spot diameter was found as 40 - 50 micrometer (FWHM) and the sevenfold growth of intensity was evaluated.
Lobster-eye optics have attracted much attention and effort in recent years due to their unique x-ray focusing capabilities. While many advances have been made in the manufacture and analysis of these optics, their characterization and the determination of their metrology remains constrained by the shortcomings of current techniques. We present a faster, better and cheaper method for the determination of many of the metrological parameters of lobster-eye optics. Optical images of the entrance and exit surfaces of an optic are taken. Applying our technique to these images allows measurement of all the geometrical properties that previously have been found to be the major contributors to focusing defects. In addition, the number of free parameters required in fitting a simulated to a measured x-ray image can be greatly reduced. We present results for the characterization of an existing lobster-eye optic and the improved modeling thereby obtained which are in very good agreement with experimental x-ray focusing data.
The prospect of making a lobster-eye telescope is drawing closer with recent developments in the manufacture of microchannel-plate optics. This would lead to an x-ray all-sky monitor with vastly improved sensitivity and resolution over existing and other planned instruments. We consider a new approach, using deep etch x-ray lithography, to making a lobster-eye lens that offers certain advantages even over microchannel-plate technology.
Anti-scatter grids are used in mammography to improve the contrast and signal-to-noise ratio by minimizing scattered x- rays. Most commercially available mammographic anti-scatter grids are one-dimensional, focused arrays of lead lamellae, sandwiched between more x-ray transparent spacer materials such as fiber or wood. Two-dimensional (2D), air-core, focused, anti-scatter grids are expected to be able to significantly reduce scatter-to-primary ratio and increase primary transmission in mammography. Two prototype unfocused, 2D, air-core nickel (Ni) anti-scatter grids were fabricated. The fabrication method uses x-ray lithography and electroplating, LIGA, which allows the fabrication of high aspect ratio metal parts. The metal parts are released from substrate. The grids have 20 micrometer thick walls and 300 micrometer period. This geometry permits 87.1% transmission of primary radiation. Each layer of the grid is assembled from nine smaller grid pieces. The assembly technique allows construction of larger grids. Grids of a desired grid height are obtained by stacking the appropriate number of layers, each layer approximately 250 - 350 micrometer thick. The first prototype is 1.48 cm X 1.48 cm and 2.00 mm high and the second prototype is 1.32 cm X 1.44 cm and 1.78 mm high. Electroplating with lead/tin will also be reported.
Refractive microcapillary lens for hard X-rays is presented. The lens is designed as glass capillary filled by a large number of biconcave microlenses. Fabrication technique for the lens is described. It is shown that the microlenses have a spherical shape. The spherical aberrations of the lens are calculated. The possibility of production of micrometer sized X-ray beams by using the microcapillary X-ray lens is discussed.
The optimization of the design of depth-graded multilayers with special angular or wavelength responses for use as coatings in EUV/X-ray optics is discussed in this presentation. The optimization is based on the well-known Fresnel equations and recursive calculation combined with a defined merit function, with random variation of the thickness of each layer. The optimization of depth-graded multilayers for various applications uses a process that judges a design based on its required performance in a given range of wavelength and/or incidence angle. The requirements could include many factors such as the spectral distribution of a source, the shape of the reflectivity curve or the geometry of the optical system. The key factor for optimization is to determine a suitable merit function for a specific application. This allows the design of multilayers for different requirements. The method has been used to give the thickness of each layer in some depth-graded multilayers with special requirements in optical properties.
A new method of design for multilayer structures with broadband spectral responses is presented. A stochastic design approach is utilized, based upon a simulated (SA) annealing algorithm, which optimizes the multilayer structure for a particular set of criteria. In particular, we consider a mirror for which the requirement is for high reflectivity, over a broad wavelength range, in the soft x-ray region, as might be compatible with the output from a laser plasma source. The design algorithm is used to maximize a merit function for the structure by manipulating the ordering, the thickness and the material types of each of the constituent layers. The merit function may also be configured to include a number of other desirable properties for the high reflectivity mirror including broad angular response, polarization response and uniformity of reflectivity over a prescribed wavelength range.
Multilayer depth-graded structures make possible creating the x-ray mirrors with the reflection angular width of about 0.2 degrees - 0.5 degrees at the wavelength of 1.54 angstrom. Special numerical optimization techniques, such as needle variations, Powell method, and some other were used to calculate the multilayer structures with desired reflection curves. It was found that for CuK radiation and the angular interval 0.5 - 0.9 degrees W-C an W-B4C structures can have the mean reflectivity about 30% with the relative deviation from uniformity better than 0.7%. Such multilayer mirrors were successfully manufactured on quartz substrates with roughness level of about 6 angstrom using magnetron sputtering technology. On this basis the first computer-driven x-ray deflector was designed and tested. For the mirror angular interval of 0.4 degree the output beam deflection interval is equal to 0.8 degree, that is enough for a variety of applications. The laboratory experiments with the deflector included the x-ray raster imaging with the resolution of about 20 micrometers, and automatic beam adjustment and re-aiming. Another possible applications are the x-ray microscopy, compensation for orbital motion of space x-ray telescopes, space x-ray communication.
We describe parabolic compound refractive lenses for hard x- rays that are genuine imaging devices similar to glass lenses for visible light. They open considerable possibilities in both full field and scanning x-ray microscopy, microanalysis, and coherent scattering. They can operate in a range from about 2 keV to 100 keV, are robust, and withstand the white beam of a third generation undulator source. Using aluminum lenses in full field microscopy a field of view of about 300 micrometer can be imaged with magnifications between 10 and 50 and a resolution of about 300 nm. With beryllium lenses an improvement of the resolution to below 100 nm is expected. For microbeam applications, the synchrotron source is imaged onto the sample in a strongly demagnifying setup. With focal distances between 0.3 m and 2 m, the source can be demagnified by a factor 20 to 200 producing a beam with lateral extensions in the micron and sub-micron range. For aluminum lenses, monochromatic microbeams with fluxes above 1010 ph/s and a gain above 1000 are routinely produced at third generation undulator sources. Compound refractive lenses will allow to produce microbeams at energies up to at least 100 keV, making for example, microfluorescence experiments at the K-edges of heavy elements possible. The modular setup of compound refractive lenses allows to adjust the focal length to ideally match the experimental requirements. Assembling and aligning the lens take about 15 minutes. No order sorting apertures are required and the straight optical path allows to remove the lens to align other components.
Silicon planar parabolic refractive lenses with relief depth of 100 micrometer are realized by microfabrication technique. A set of 5 planar lenses with simple parabolic profiles and equal apertures and equal focal distances is realized. This set consists of different number (from 1 to 8) of individual lenses. Lenses with minimized absorption as a set of parabolic segments are fabricated too. Focusing and spectral properties of silicon planar parabolic lenses were studied with synchrotron radiation in the x-ray energy range 8 - 25 keV at the ESRF. Linear focus spots of 1.5 micrometer width were recorded for the parabolic lenses and 1.8 micrometer for the lenses with minimized absorption. The intensity transmission of the lens with minimized absorption is two times greater than this value of simple parabolic lenses at 8 keV and in the x-ray energy range over 15 keV overcomes 90%. Spectral properties of the lenses with minimized absorption are discussed in details. Heatload properties of the silicon planar lenses are analyzed and compared with the lenses made of diamond.
A refractive lens for hard X-rays comprising two saw-tooth profiles is presented. This lens has the same focusing properties as a parabolic compound refractive lens. One advantage is the remarkably low fabrication cost, since curved surfaces are replaced by planar ones. In addition, the focal length of the lens can be easily varied by adjusting the angle between the two halves. Since the index of refraction depends on the X-ray energy, the lens is chromatic and acts as a band- pass filter for a broad energy spectrum. Combined with the tunability of the focal length, this allows versatile spectral shaping of the X-ray beam. Calculations and numerical examples of the focusing properties are presented. Due to its low atomic number, beryllium is an excellent choice for refractive optics and a prototype in beryllium has been fabricated using diamond turning technique. Surface metrology shows a deviation from the ideal shape of about 400 nm rms, indicating a loss of intensity of between 20% and 50%, depending on the geometry an X-ray energy.
Zone plates as used in high resolution x-ray microscopy have focal lengths which are proportional to the x-ray energy. This means that in techniques such as elemental and chemical state mapping, which require images to be made at more than one energy, refocusing is required which can lead to loss of image registration. Using two zone plates, in a similar fashion to achromatic refractive lens doublets for visible light, it is possible to focus two x-ray energies to the same spot.
An x-ray zone plate was fabricated using the novel approach of focused ion beam (FIB) milling. The FIB technique was developed in recent years, it has been successfully used for transmission electron microscopy (TEM) sample preparation, lithographic mask repair, and failure analysis of semiconductor devices. During FIB milling, material is removed by the physical sputtering action of ion bombardment. The sputter yield is high enough to remove a substantial amount of material, therefore FIB can perform a direct patterning with submicron accuracy. We succeeded in fabricating an x-ray phase zone plate using the Micrion 9500HT FIB station, which as a 50 kV Ga+ column. Circular Fresnel zones were milled in a 1.0-micrometer-thick TaSiN film deposited on a silicon wafer. The outermost zone width of the zone plate is 170 nm at a radius of 60 micrometer. An achieved aspect ratio was 6:1.
High resolution and high efficiency Zone Plate for X-rays in the energy range of 300 eV and 12 KeV fabricated by means of electron beam and X-ray lithography are presented. Regarding the high resolution regime zone plate with 40 nm outermost zone and thickness of 0.2 micrometer are shown. For high efficiency performances, multilevel zone plate and continuous profile were fabricated to provide an increase of efficiency at the first diffraction order and to suppress higher ones. The combination of the two lithography allows a powerful design flexibility at several energy regimes.