S. Kuznetsov

X-ray refractive planar lens with minimized absorption

Silicon refractive planar parabolic lenses with minimized absorption were fabricated by a combination of photolithography and dry-etching techniques. Focusing and spectral properties of the lenses were studied with synchrotron radiation in the energy range 8–25 keV at the European Synchrotron Radiation Facility. A focal spot of 1.8 μm with a gain of 18.5 and transmission of more then 80% was measured at 15.6 keV. The spectral characteristics were analyzed taking into account material dispersion and photon-energy attenuation in the hard x-ray range.

X-ray focusing by planar parabolic refractive lenses made of silicon

Abstract First refractive planar parabolic lenses are realized in Si. They comprise a set of parabolic profiles (planar parabolic lenses) or parabolic segments (planar parabolic lenses with minimized absorption) with symmetry axis lying in Si wafer surface plane. The relief depth achieved by dry etching processes is 100 μm. Experimental testing of lenses has been carried out on an RU-200 rotating anode generator with CuKα radiation (8.05 keV). The focal length, estimated and confirmed by experiment, is F=18 cm for planar parabolic lenses. The lenses with minimized absorption have shorter focal length F=16.8 cm, showing a 5 μm recorded source image. The calculated transmission for these lenses reaches T=37%, approaching values of transmission for compound refractive lenses made of low Z materials.

On the requirements to the instrumentation for the new generation of the synchrotron radiation sources. Beryllium windows

Abstract It was shown that the high spatial and time coherency of the X-ray beam delivered at the ESRF allows one to observe very weak perturbation of the wave front, resulting in the phase contrast and undesirable speckle structure of the beam, that impose special requirements to all elements to be installed in the optical path such as beryllium windowns, filters and mirrors. The contrast from existing beryllium windows at the ESRF beamlines and specially polished Be foils was experimentally studied at an energy range from 10 to 20 keV. It was revealed that the uneven surface of the beryllium windows leads to a beam structure with intensity changes up to 50–100%. The theory of the phase contrast imaging by a transparent object was presented and some theoretical estimations were made to formulate the requirements imposed on the roughness of the Be window surface to avoid the unwanted deterioration of the beam spatial coherence.

X-ray multilens interferometer based on Si refractive lenses

We report a multilens X-ray interferometer consisting of six parallel arrays of planar compound refractive lenses, each of which creates a diffraction limited beam under coherent illumination. Overlapping such coherent beams produces an interference pattern demonstrating substantially strong longitudinal functional dependence. The interference fringe pattern produced by multilens interferometer was described by Talbot imaging formalism. Theoretical analysis of the interference pattern formation was carried out and corresponding computer simulations were performed. The proposed multilens interferometer was experimentally tested at ID06 ESRF beamline in the X-ray energy range from 10 to 30 keV. The experimentally recorded fractional Talbot images are in a good agreement with computer simulations.

Silicon planar parabolic lenses

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.

High energy X-ray nanofocusing by silicon planar lenses

Optimizing the lens design and improving the technological process, we manufactured X-ray planar compound refractive lenses with vertical sidewalls up to 70 microns deep. The lens surface roughness in the order of 20 nm was attained. The minimal thickness of the material between two individual lenses of 2 μm was realized. The optical tests of the new planar lenses were performed at the ESRF BM05 and ID15 beamlines. The technological breakthrough allows reaching the nanometer focusing. The resolution below 200 nm was measured in the energy region of 15–80 keV. The best resolution of 150 nm was demonstrated at 50 keV X-rays.

Silicon planar lenses for high-energy x-ray nanofocusing

Optimizing the lens design and improving the technological process, we manufactured X-ray planar compound refractive lenses with vertical sidewalls up to 70 microns deep. The lens surface roughness in the order of 20 nm was attained. The minimal thickness of the material between two individual lenses of 2 µm was realized. Driven by the requirements of new 100 m-long beamlines at the ESRF, the first prototype chip of Si planar nanofocusing lenses was designed and manufactured. The technological breakthrough allows to reach the nanometer focusing. The optical tests of the new planar lenses were performed at the ESRF beamlines BM5 and ID15. The resolution below 200 nm was measured in the energy region of 15-80 keV. The best resolution of 150 nm was demonstrated at 50 keV energy. As a next step dedicated chip design for two-dimensional focusing with nanopositioning stages will be realized.

Planar parabolic lenses for focusing high-energy x-rays

Microelectronics technology involving photolithography and highly anisotropic plasma etching techniques was applied to fabricate planar parabolic refractive lenses. A set of Si planar parabolic lenses with apertures from 0.5 to 1.8 mm and 200 microns deep has been fabricated especially for high energy X-rays (E > 50 keV). Focusing properties in terms of the spot size and the efficiency in the energy range from 50 to 100 keV have been studied at the ESRF ID15 beamline. Linear focusing by single lens and by two-lens system as well as two-dimensional focusing by two lenses in cross geometry has been realized. Features of refractive collimator based on a set of planar lenses have been investigated and a technique for evaluation of the beam divergence in a micro radian range has been proposed. Future applications of proposed planar lenses are discussed.

Hard x-ray single crystal bi-mirror.

We report a novel hard x-ray interferometer consisting of two parallel channels manufactured in a single Si crystal by means of microfabrication technology. The sidewall surfaces of the channels, similar to mirrors, scatter at very small incident angles, acting equivalently to narrow micrometer size slits as in the Young double-slit interferometer. Experimental tests of the interferometer were performed at the ESRF ID06 beamline in the energy range from 12 to 16 keV. The interference patterns at different grazing incidence angles were recorded in the near- and far-field. Evaluation of the influence of the channel surface roughness on the visibility of interference fringes was performed. The proposed interferometer design allows the arrangement of mirrors at different split distances.

Refractive and diffractive X-ray optical elements.

The planar microelectronics technology, involving lithography and highly anisotropic plasma etching techniques, allows manufacturing high quality refractive and diffractive lenses, which may be used in hard X-ray microprobe and microscopy applications. These silicon lenses are mechanically robust and can withstand high beat load of the white X-ray beam at third generation synchrotron radiation sources. For the first time we designed and manufactured a new type of lenses: kinoform lenses and parabolic lenses with scaled reduction of curvature radii. The theoretical background for such type of lens features is presented. Focusing properties in the terms of focus spot and efficiency of all these lenses were tested at the ESRF beamlines. Magnified imaging with planar lense was realized. Some future developments are discussed.