At the Institute of Microstructure Technology (IMT) at Karlsruhe Institute of Technology (KIT), refractive X-ray optics are developed. These optics are proposed to be used as condenser optics in X-Ray spectroscopy and microscopy applications with an X-ray tube as a source. To produce the lenses, a thin structured foil with equidistant fins in triangular form is casted from a structured silicon wafer. The foil is then wound around a glass fibre core. Due to this fabrication method, it is possible to produce large-aperture lenses with low absorption in comparison to other types of refractive X-Ray optics, like X-ray lenses with continuous parabolic shape or prism lenses. The first are limited due to their absorption while the latter are limited due to their mechanical stability of the prism columns. The optimisation of the so called X-Ray rolled prism lenses (RXPL) is underway at the institute and involves several parameters. One important property of the lenses is the correct form of the wound foil layers. This determines the number of necessary refractive elements at a given radius, which in turn determines the refracted slope and focal position of the transmitted beam. The spatial extent of the x-ray source is also being accounted for in the lens design. Another important point is the diameter of the winding core, which should be as small as possible due to the fact that the winding core reduces the active area of the lens. The rolling process itself is also revised to produce lenses with the above-mentioned small diameter winding cores and bend foil layers while sustaining a tight- fitting foil bundle. The lenses are studied at different energies and types of X-Ray tubes, as well as synchrotron sources, to gain additional information of the internal structure of the lens after the winding process. In this paper the current status of the lens development and results at X-Ray tube sources for use in diffractometers is presented.
At the Institute of Microstructure Technology (IMT) at Karlsruhe Institute of Technology (KIT) X-ray refractive line
focus lenses have been developed. They consist of a large number of concave bi-parabolic lens elements made of SU8.
To form a point focus two of these lens stacks, tilted by 90° with respect to each other around the optical axis, need to be
arranged in the optical path. To increase their transmission, the Fresnel principle can be applied to the lenses to provide
higher ratios of refractive power to absorption. The lenses are fabricated by deep X-ray lithography which allows to
pattern high aspect ratio structures and gives the possibility to fabricate the lens elements tilted by 90° with respect to
each other on a single substrate by tilted double exposure. Nevertheless, the aspect ratio is limited, due to the fact that the
columns tend to collapse from capillary forces during fabrication if they exceed a certain height. To overcome this issue
and to simplify the fabrication process a new type of lenses as well as a method to fabricate refractive large aperture
lenses has been developed recently at IMT. These lenses are fabricated out of a structured polyimide film which is cut
into a calculated shape and rolled around a glass-fiber core. The structure on the film itself consists out of triangular
shaped ribs. The lenses provide the advantage of Fresnel lenses and also provide a point focus through their approximate
rotational symmetry. The full width at half maximum (FWHM) of the focal spot of such lenses is mainly determined by
the height of the triangular ribs. Such X-ray optical elements are well suited to be used as condenser lenses, because they
provide efficient illumination of an area in the exit working distance. To increase the lens performance, the lens
fabrication process has been optimized. In the paper we provide information on how the lenses where improved and
present results from tests with X-ray tube sources.
The unique beam characteristics of PETRA III at DESY promote novel applications for many scientific fields,
including imaging applications. For tomography these are techniques like high-speed and in-situ measurements
marked by highest density resolutions and spatial resolutions down to the nanometer range. Furthermore, the
high coherence enables phase contrast applications in an exceptional way. Therefore, the Imaging Beamline IBL
is equipped with two dedicated endstations, one for micro and one for nano tomography. In addition, a very
flexible X-ray and light optics concept is implemented. The micro tomography endstation is designed for samples
requiring (sub-) micrometer resolution. The technical specifications of the nano tomography endstation aim for
a spatial resolution of below 100 nm. The nanometer resolution will be achieved by using different combinations
of compound refractive lenses as X-ray optics. The overall setup is designed to be very flexible, which allows
also the implementation of other optical elements as well as the application of different magnifying techniques.
Refractive X-ray lenses can be used effectively, to focus or collimate X-rays with photon energies clearly above 10 keV.
On the one hand parabolic Compound Refractive Lenses (CRLs) are suitable as imaging optics in high resolution X-ray
microscopy. The most recent developments are nanofocusing refractive X-ray lenses (NFLs). These show focal spot
sizes of less below 100 nm. On the other hand refractive X-ray lenses can provide a high photon flux when used as large
aperture condenser optics. Two types of refractive condenser optics made out of structures with triangular profile have
been developed at the Institute for Microstructure Technology (IMT) at the Karlsruhe Institute of Technology (KIT) and
have been tested at synchrotron sources in recent years. One type of special interest is the Rolled X-ray Prism Lens
(RXPL). These lenses are made of a rolled polymer foil structured with micro grooves with triangular profile. The
combination of such condenser optics and NFLs provides a basis for future hard X-ray microscopes.
X-ray prism lenses have been defined with the aim to collimate X-ray radiation emitted from an X-ray tube working as a
condenser lenses. Such a lens must have a large aperture as low absorption as possible. X-ray prism lenses combine low
absorption and large apertures. They are made up of a large array of equilateral triangular prismatic microstructures. The
intent by using these structures is to obtain as many refracting surfaces as possible in the smallest volume. The higher
surface-volume-ratio in comparison to standard lenses reduces absorption significantly at the expense of focus quality.
A first lens has been fabricated by X-ray lithography out of PMMA, with a designed aperture of up to 1.4 mm working
distances of 325 mm to the point source and X-ray energy of 9 keV. The edge-length of the prismatic microstructures is
10 μm. The lenses have been tested at the ESRF in (Grenoble, France) and at ANKA (Karlsruhe, Germany). The results
show an influence of the imperfections of the lens structures (bended prismatic microstructures) on the focal spot along
the focal line. The measured gain was 28 at a focal width of 8 μm at full width at half maximum. Due to these
imperfections the relevant aperture is currently limited to 500 μm.
We develop a new type of X-ray lens system which is achromatic in a limited energy range. For such achromats
we combine different types of refractive and diffractive elements. For example, Fresnel zone plates and planar
parabolic concave SU-8 lenses are combined with lenses with a biconvex parabolic shape and with Fresnel lenses,
respectively. We present numerical results from a theoretical study of such optical systems. We determine the
focal spot size for an energy range of about E ± ΔE with ΔE/E ≈ 17%. Amongst other results we find that, compared with conventional lens systems, the spot size can be reduced by several tens of percent by using such achromatic lens systems.
Over the last decade refractive lenses for monochromatic X-ray radiation have been realized for many different materials by microfabrication technology. All these lens systems are successfully working only for one discrete energy, i.e. the lenses are chromatic. Thus each discrete energy within a certain energy range has a different focal length. While the focal spot size is smaller than a micron for a particular energy at the corresponding focal
distance, it increases up to several tens of microns for a larger energy range. We present results of numerical simulations for a new type of lens system which addresses this problem. We are developing achromats by combining different refractive elements of different materials. Via ray-tracing we determine the parameters of
the lenses by minimizing the focal spot size for an energy range of about E ± ΔE with ΔE = 15%. Thus the spot size of an energy range can be noticeably reduced compared with conventional refractive (chromatic) lens systems.
Existing refractive X-ray lenses are characterized by either small apertures due to high absorption in the border areas. They can only be used with synchrotron sources, offering high brilliance. By increasing transparency and aperture the range of applications will expand, common X-ray tubes might turn out to be reasonable X-ray sources in an application with X-ray lenses. A basic concept that meets the demands is an X-ray Fresnel lens. But, Fresnel X-ray lenses are hard to fabricate, since the smaller lens structures need to be produced with extremely high aspect ratios. As an alternative, the
Fresnel structures can be replaced by an array of prism-shaped structures. In particular equilateral triangular structures are easier to fabricate and additionally give a higher
surface-volume-ratio, increasing transparency. At the Institute for
Microstructure Technology the development of such prism lenses is under way. Due to the physical properties of X-rays, several thousands of precisely arranged prisms with large aspect ratio and smooth sidewalls are needed for a single X-ray lens. Therefore, direct X-ray lithography is used to fabricate the SU-8 microstructures. The length of one single prism edge is of the order of 10 μm. One single prismatic X-ray lens consists of up to 60.000 prisms. With the appropriate X-ray mask, refractive X-ray lenses with an aperture of up to 2 mm, for a source distance of 350 mm and a working distance of 350 mm are being produced, assuming a point-shaped source. These X-ray prism lenses are not optimized for
smallest focal diameter, but designed to illuminate samples in X-ray optical systems. Most important in this application is an as high transparency as possible.
We present results on comprehensive studies of high resolution SU-8 planar refractive lenses. Lens optical properties were investigated using coherent high energy X-ray radiation. Resolution of about 270 nm was measured for the lens consisting of 31 individual lenses at energy 14 keV. Coherent properties of the set-up permit to resolve near-focus fine structure, which is determined by tiny aberrations caused by lens imperfections close to the parabola apex. This study allows understanding as far SR deep lithography as possible can maintaine to close tolerances for lens parameters. Two-dimensional focusing crossed lenses were tested and imaging experiments in projection and imaging mode were conducted. Radiation stability test was performed and conclusions on the applicability of SU-8 lenses were done.
Sets of planar SU-8 cross lenses focusing in two directions have been fabricated by tilted deep X-ray lithography using an X-ray mask with tilted absorber structures. The profile of the absorber structures on the mask take into account the lithographic peculiarities of SU-8 resist to reproduce the designed profile of the lens elements exactly. The cross lenses are placed on one substrate and have identical focal distances, which allow to scan the spectral range from 5 keV to 30 keV by stepping the lens substrate from one lens to the next. Another set of cross lenses was developed with different quasi-parabolic profiles to obtain a large focus depth (up to several centimeters) with uniform intensity distribution in the micron focal spot. This together with the stepping possibilities between lenses satisfies the requirement of static spectroscopy experiments. For the truncated parabolic profile, these cross lenses consist of separate segments arranged in a new mosaic form. In comparison with the known “fern”-like kinoform profile, the lenses have been developed with smaller gain loss. The testing of the new sets have been performed at the undulator ID-18F and ID-22 beamlines (ESRF, Grenoble, France) and the experimental results are compared to simulations.
We report the results on experimental study of optical properties of Ni refractive lenses made by deep X-ray lithography and LIGA techniques. One- and two-dimensional lenses were tested at the ESRF ID15 beamline using wide energy spectrum from 40 keV to 220 keV. The focusing properties in terms of focal length, size of the focal spot/line and gain were studied. Sub micrometer focusing was measured in the energy range from 40 to 150 keV. The measured lens parameters were compared with ray-tracing analysis.
Compound refractive lenses printed in Al and Be are becoming the key X-ray focusing and imaging components of beamline optical layouts at the 3rd generation synchrotron radiation sources. Recently proposed planar optical elements based on Si, diamond etc. may substantially broaden the spectrum of the refractive optics applicability. Planar optics has focal distances ranging from millimeters to tens of meters offering nano- and micro-focusing lenses, as well as beam condensers and collimators. Here we promote deep X-ray lithography and LIGA-type techniques to create high aspect-ratio lens structures for different optical geometries. Planar X-ray refractive lenses were manufactured in 1 mm thick SU-8 negative resist layer by means of deep synchrotron radiation lithography. The focusing properties of lenses were studied at ID18F and BM5 beamlines at the ESRF using monochromatic radiation in the energy range of 10 - 25 keV. By optimizing lens layout, mask making and resist processing, lenses of good quality were fabricated. The resolution of about 270 nm (FWHM) with gain in the order of 300 was measured at 14 keV. In-line holography of B-fiber was realized in imaging and projection mode with a magnification of 3 and 20, respectively. Submicron features of the fiber were clearly resolved. A radiation stability test proved that the fabricated lenses don't change focusing characteristics after dose of absorbed X-ray radiation of about 2 MJ/cm3. The unique radiation stability along with the high effficiency of SU8 lenses opens wide range of their synchrotron radiation applications such as microfocusing elements, condensers and collimators.
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.
Ablation of fluorine-containing polymers is studied under the influence of ionizing roentgen radiation. Physical-chemical properties of the polymers FEP and PVDF irradiated with synchrotron radiation were investigated. When film temperature increases because of the irradiation, intense removing of the polymer proceeds with high selectivity. Polymer membranes with regular disposition of through pores were created in the absorbing layer of submicron size in the process of irradiation of fluorine-containing films through a mask with regular holes.
Development of the present-day technologies of manufacturing deep structures with submicron elements based on the deep x- ray lithography method with the usage of synchrotron radiation. Microelectronics used x-ray patterns with a 1.0 micrometers golden masking covering on different-type membranes become of unfit in this case both from the angle of contrast and from the standpoint of radiation and heat stability. X- ray patterns with the membrane on the base of tantalum 2 micrometers thick, that are high contrasting as to synchrotron radiation with wavelength of 0.2 to 1.0 nm, have been developed and manufactured. A set of pores 0.7 micrometers in diameter 1.5 micrometers apart in two directions was formed as the topological pattern.
The phenomenon of anisotropic ablation of PTFE under SR is studied. Heat conductivity and melting point of PTFE came down under irradiation. The possibility of SR-assisted formation of regular microporous membranes with average diameter of 0,5 micrometers of the pores in PTFE films is investigated.
G. Kulipanov, Oleg Makarov, Lubov Mezentseva, S. Mishnev, Vladimir Nazmov, Valery Pindyurin, A. Skrinsky, L. Artamonova, G. Cherkov, V. Gashtold, V. Prokopenko, Vladimir Chesnokov, Elena Reznikova
The X-ray lithography with synchrotron radiation at the VEPP-3 storage ring was applied for fabrication of polymer microstructures with submicron sizes of elements and with rather high aspect ratio (up to 20). The microstructures are the regular microporous membranes with pores of 0.3-0.5 micrometers in diameter arranged with a 1 micrometers spacing. The membranes were fabricated on a base of 2.5, 3, 6 and 10 micrometers thick mylar films. In contrast to the commercial track membranes with random pore locations, the regular membranes have no dispersion of pore sizes caused by confluence of adjoining pores. The fabricated membranes have a porosity of 10-20 percent and this value can be increased up to 50 percent and higher by using an X-ray mask with an appropriate pattern. The results of the membrane examination by different techniques are presented. Possible improvements of the membrane parameters and some potential applications of the membranes are discussed as well.
X-ray lithography with synchrotron radiation was applied for formation of the Fresnel zone structure profile onto a curved surface of a refractive polymer lens to achieve multifocus properties of the lens. First prototypes of the hybrid refractive-diffractive lens were fabricated in such a way and their optical properties were investigated. Some possibilities for creation of diffraction apochromatic optical elements are considered as well.
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