We report the manufacture and experimental tests of first diamond refractive lenses for hard X-ray focusing. A transfer molding technique based on diamond growth on a pre-patterned silicon mould was employed to fabricate diamond refractive lenses. Diamond films were produced by microwave plasma enhanced chemical vapor deposition. The lenses were designed for 50 cm focal length at energy 9 keV. Experimental tests were performed at the ESRF ID15 (wiggler) and ID22 (undulator) beamlines using monochromatic, "pink" and white X-ray radiation in the energy range from 6 to 40 keV. Focusing in the order of 1-2 microns was achieved. To evaluate the lens microstructure properties phase contrast imaging and diffraction techniques (SAXS and WAXS) were applied.
Recently, we have been able to fabricate high quality parabolic refractive x-ray lenses made of beryllium. We report first experimental results in both full field microscopy and microbeam production using these new lenses. In full field microscopy, undistorted images of test patterns were recorded in a field of view of 450 μm full width half maximum at 12keV with 10 fold magnification. A significant improvement of the lateral resolution as compared to imaging with aluminium refractive lenses was achieved. Microbeam characteristics were determined at 12keV demagnifying a high β undulator source 82 times. The lateral beam size was measured by fluorescence knife-edge. Microbeam characteristics, such as flux, lateral beam size, and low intensity background are discussed.
We demonstrate that Si planar parabolic lens with long focus distance can collimate high energy X-rays with microradian precision. A divergent beam from a wiggler at the ESRF ID15 beamline is reduced from 15 microradian down to 1 microradian. We propose a new imaging technique for direct measurements of beam divergence. It is shown experimentally that precision better than 1 mrad may be really achieved. Measurements are done at the energy range 60 - 90 keV. Contribution of source size and diffraction phenomena to the precision and ultimate sensitivity of the developed technique is discussed.
Refractive x-ray lenses have been fabricated using deep x-ray lithography. Lenses were produced directly in 1- to 6-mm-thick sheets of polymethylmethacrylate (PMMA) with as many as 100 cylindrical lenses along the optical axis. The fabrication process consists of exposing the PMMA sheets to high-energy synchrotron radiation through a mask of 50-micron-thick gold on silicon, and subsequent development in ketone. The lenses are suitable for use in synchrotron radiation from a bending magnet at the Advanced Photon Source in the energy range of 8-16 KeV. Results of measurements of focus quality, flux density gain, and scatter are presented and discussed with regard to the quality of lens material and fabrication method. Means for improving the performance of the lenses is discussed.
Saw-tooth refractive x-ray lenses have been used to focus a synchrotron beam to sub-μm line width. These lenses are free from spherical aberration and work in analogy with 1-D focusing parabolic compound refractive lenses. However, the focal length can be varied by a simple mechanical procedure. Silicon lenses were fabricated by wet anisotropic etching, and epoxy replicas were molded from the silicon masters. Theses lenses provided 1-D intensity gains up to a factor of 40 and the smallest focal line width was 0.74 μm, very close to the theoretical expectation. Two crossed lenses were put in series to obtain 2-D focusing and the 80 μm by 275 μm source was imaged to 1.0 μm by 5.4 μm. Beryllium lenses were fabricated using conventional computer-controlled milling. The focal line width was 1.7 μm, nearly 3 times larger than predicted by theory. This can be attributed to large surface roughness and a bent lens shape.
Design, fabrication, testing, and performance of an x-ray lens assembly are described. The assembly consists of a number of precisely stacked and aligned parts, each of which is a section of an extruded aluminum piece having 16 parabolic cavities. The wall thickness between adjacent cavities is 0.2 mm. By stacking a number of long, extruded parts and cutting the assembly diagonally, a variable-focus lens system is derived. Moving the lens horizontally allows the incident beam to pass through fewer or more cavities focusing the emerging beam at any desired distance from the lens.
The variable focus aluminum lens has been used at the Advanced Photon Source to collimate a monochromatic, 8 keV undulator beam. Results indicate collimation consistent with theoretical expectations.
X-ray refractive optics is mainly concerned on a focusing devices. Another kinds of X-ray refractive devices with a new functionality, namely X-ray biprism and Michelsone echelon are considered. An experiment was fulfilled with biprism made from the synthetic diamond crystals on BM05 beamline ESRF. A computer simulation technique was developed to obtain interference patterns generated by the biprism with an account of a variety of experiment geometrical conditions, source size and absorption in biprism material. Recorded interference patterns were in a good agreement with the predicted ones for a given experimental conditions. Thus a complete description of a brightness distribution in source can be obtained by a reconstruction of the intensity distributions in interference fringes using the developed technique for investigation of synchrotron beams coherence. Possibilities of devices realisation with a extended functional capabilities by means of previously used microelectronic planar techniques are discussed.
We report the design and construction of an off-axis zone-plate monochromator for diffraction-imaging experiments at beam line 9.0.1 at the Advanced Light Source (ALS) synchrotron-radiation facility at Berkeley USA. The device is based on an off-axis zone plate which can be conveniently inserted into or retracted from the beam. We discuss design issues such as the efficiency and spectral purity of the system and the technique for designing heat-tolerant windows for soft x-ray undulator beams. The monochromator functions successfully and good-quality diffractions patterns are being made with the beam it delivers.
We use Fresnel zone plates as focusing optics in hard x-ray microprobes at energies typically between 6 and 30 keV. While a spatial resolution close to 0.1 μm can currently be achieved, highest spatial resolution is obtained only at reduced diffraction efficiency due to manufacturing limitations with respect to the aspect ratios of zone plates. To increase the effective thickness of zone plates, we are stacking several identical zone plates on-axis in close proximity. If the zone plates are aligned laterally to within better than an outermost zone width and longitudinally within the optical near-field, they form a single optical element of larger effective thickness and improved efficiency and reduced background from undiffracted radiation. This allows us both to use zone plates of moderate outermost zone width at energies of 30 keV and above, as well as to increase the efficiency of zone plates with small outermost zone widths particularly for the energy range of 6 - 15 keV.
Fabrication of Fresnel zone plates for the hard x-ray spectral region combines the challenge of high lateral resolution (~100 nm) with a large thickness requirement for the phase-shifting material (0.5-3 μm). For achieving a high resolution, the initial mask was fabricated by e-beam lithography and gold electroforming. To prevent the collapse of the structures between the developing and electroforming processes, drying was completely eliminated.
Fabrication errors, such as nonuniform gold electroplating and collapse of structures, were analyzed and systematically eliminated. We optimized the exposure and developing processes for 950k and 2200k polymethylmethacrylate of different thicknesses and various adhesion promoters. We discuss the effects of these fabrication steps on the zone plate's resolution and aspect ratio. Fresnel zone plates with 110 nm outermost zone width, 150 μm diameter, and 1.3 μm gold thickness were fabricated. Preliminary evaluation of the FZPs was done by scanning electron microscopy and atomic force microscopy. The FZP focusing performance was characterized at the Advanced Photon Source at Argonne National Laboratory.
Circular and linear zone plates have been fabricated on the surface of silicon crystals for the energy of 8 keV by electron beam lithography and deep ion plasma etching methods. Various variants of compound zone plates with first, second, third diffraction orders have been made. The zone relief height is about 10 mkm, the outermost zone width of the zone plate is 0.4 mkm. The experimental testing of the zone plates has been conducted on SPring-8 and ESRF synchrotron radiation sources. A focused spot size and diffraction efficiency measured by knife-edge scanning are accordingly 0.5 mkm and 39% for the first order circular zone plate.
We studied the feasibility to create a Bragg-Fresnel optical element through the use of silicon dioxide films grown on the silicon perfect crystal surface. In our case the Bragg-Fresnel lens structure consists of a set of silicon dioxide rectangular shape etched zones arranged by the Fresnel zone law. The stress within coated and uncoated crystal regions is opposite in sign, whether tensile or compressive. The strain in the substrate crystal lattice directly underneath discontinuities in the deposited film give rise to phase difference between waves diffracted from coated and uncoated crystal regions. This phase difference is known to be dependent on the thickness and composition of film and substrate. In this paper the focusing properties of Si/SiO2 Bragg-Fresnel lenses with 107 zones and 0.3 micrometer outermost zone width were experimentally studied as a function of the silicon oxide thickness in the range of 100 - 400 nanometers. The efficiency of the focusing of hard X-rays was found to be about 16% at energy 10 keV.
In our days, there is an increased interest for extreme ultraviolet and x-ray microscopy, which is mainly due to the availability of nearly ideal optical sources for diffractive optics. Synchrotrons of the latest generation and free electron lasers (in the near future) are sources that can produce x-ray beams with low divergence, whose wavelength can be tuned over a range of several keV and whose spectrum can be monochromatised within a band pass Δλ/λ< 10-4. In this paper we present the design, fabrication and use of novel diffractive optical elements that, beyond simple focusing, can perform new optical functions in the range of soft X-rays: multi-focusing in single or multiple focal planes and beam shaping of a generic monochromatic beam into a desired continuous geometrical pattern. The design is based on scalar diffraction approaches using iterative or direct algorithms to calculate the optical function. Diffractive optical elements with 100x100 microns size and 100 nanometers resolution have been fabricated using e-beam lithography and their optical functions have been tested in differential interference contrast microscopy. We suggest their use also in mask-less lithography and chemical vapor deposition induced by extreme ultraviolet and x-ray radiation.
The manipulation of x-rays by phase structures is becoming more common through devices such as compound refractive lenses, blazed zone-plates and other structures. A spiral phase modulation structure can be used to condition an x-ray beam to produce an x-ray vortex. An x-ray beam in this form can be used as the first step towards a self-collimating beam. Also it can be used as a controllable pathological feature in studies of x-ray phase retrieval.
We describe the microfabrication of a spiral phase modulation structure by excimer laser ablation. A multi-step fabrication using 15 separate chrome-on-quartz mask patterns is used to create a 16 step spiral staircase structure approximating the desired spiral ramp. The results of simulations and initial experimental results are presented.
We present a new concept for an X-ray analyzer for meV-spectroscopy with hard X-rays in the range of 20 keV. The analyzer consists of a 5"-diameter planar glass disk with about 8000 silicon crystal pixels glued to it. With a spherical bender it is bent to a radius of 6 m. The slope error over a 4"-diameter area is about 0.8 μm RMS. Used in a spectrometer for inelastic X-ray scattering as an analyzer, an overall energy resolution of 1.0 meV at 25.7 keV and of 1.8 meV at 21.6 keV is obtained.
Spherically bent silicon crystal x-ray analyzers have been employed in high-resolution inelastic x-ray scattering experiments to increase the counting efficiency due to the small cross-section of the inelastic scattering processes of interest.  In these bent analyzers, strain causes a distribution of lattice spacing, limiting the achievable energy resolution. Hence, the silicon wafers were diced using precision diamond saws into an array of ~1x1 mm2 blocks, and then acid etched to remove the saw damage, leaving blocks ~0.6x0.6 mm2 glued to a spherical concave substrate. With this method, meV energy resolution has been demonstrated with a bending radius of 6.5 m. 
We seek to optimize the dicing process using the technique of deep reactive ion etching (DRIE) to develop highly efficient crystal analyzers. Ideally, each individual block subtends an angle that matches the acceptance (Darwin width) of the silicon reflection. This requires block sizes of about 500 μm2. DRIE offers the flexibility of selecting the block size, with finely controlled groove widths (i.e., minimal loss of material), and hence the possibility of controlling the energy width.
We have made a prototype analyzer using DRIE with block size of 470 μm2, groove widths of 30 μm, and about 500 μm deep. The wafer was then bent and glued to a glass substrate with 2-meter radius. Tests showed encouraging results, with the DRIE analyzer performing at the 100 meV level. Details of the process and further refinements will be discussed.
Following successful experience using photolithography and high aspect ratio reactive ion etching (RIE) to produce dynamically bent x-ray sagittal focusing crystals, we report on incorporating this optic in a novel high flux, narrow bandwidth, energy scanning monochromator for bend magnet synchrotron radiation. We describe the mono, several modes of operation, and our experience using it. Deep RIE has great utility for the manufacture, in silicon, of mechanical devices with feature as small as a few microns, however aberration free Bragg diffraction focusing requires uniformity in etch depth over large areas. To improve optical performance in terms of minimum focus spot size and maximum x-ray throughput, we are developing "second generation" focusing crystals based on a composite structure concept. We describe some of this new work and suggest areas of application.
We are developing freestanding high-aspect-ratio, focused, two-dimensional antiscatter grids for mammography using deep x-ray lithography and copper electroforming. The exposure is performed using x-rays from bending magnet beamline 2-BM at the Advanced Photon Source (APS) of Argonne National Laboratory. A 2.8-mm-thick prototype freestanding copper antiscatter grid with 25μm-wide parallel cell walls and 550 μm periodicity has been fabricated. The progress in developing a dynamic double-exposure technique to create the grid with the cell walls aligned to a point x-ray source of the mammography system is discussed.
We report on the progress in innovative X-ray mirror development with focus on requirements of future X-ray astronomy space projects. Various future projects in X-ray astronomy and astrophysics will require large light-weight but highly accurate segments with multiple thin shells or foils. The large Wolter 1 grazing incidence multiple mirror arrays, the Kirkpatrick-Baez modules, as well as the large Lobster-Eye X-ray telescope modules in Schmidt arrangement may serve as examples. All these space projects will require high quality and light segmented shells (shaped, bent or flat foils) with high X-ray reflectivity and excellent mechanical stability.
We have perfected a micromachining technology based on microlithography and electroforming for producing uniformly redundant arrays (URA) and Young's slits for coherence measurements in synchrotron radiation beamlines. The structures may act as absorbent objects or as phase objects. Two microfabrication techniques were used. Optical lithography in thin photoresists followed by gold electroforming on silicon nitride membranes produced structures 0.5-2.0 μm thick. Soft x-ray lithography in thick resists using the structures produced by optical lithography as a mask, followed by gold electroforming, produced structures up to 6.3 μm thick. Young's slits, one dimensional (1D), and two dimensional (2D) URA structures with feature sizes as small as 1 μm were produced in this way and used for coherence measurements in the soft and hard x-ray regimes at the Advanced Photon Source.
X-ray kinoform lenses were proposed earlier as focusing devices with refractive and diffractive properties. Deep X-ray lithography technique was applied to realize kinoform lenses in thick resist layers PMMA. Created lens has rather short focal distance 20 cm at base energy 17.5 keV and full aperture 1.5mm with outermost segments 2 μm in width. Predicted performance of created lens is compared with simple parabolic lenses. Applications of kinoform lenses are considered and potentials of X-ray lithography for creation new versions of refractive focusing devices are discussed.