Vladimir Nazmov

Planar sets of cross x-ray refractive lenses from SU-8 polymer

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.

Parabolic crossed planar polymeric x-ray lenses

The principles of design and manufacturing of the polymer planar x-ray lenses focusing in one and two directions, as well as the peculiarities of optical behaviors and the results of the lens test are reported in this paper. The methods of electron and deep x-ray lithography used in lens manufacturing allow the manufacture of ten or more x-ray lenses on one substrate; the lenses show focal lengths down to several centimeters for photon energies between 5 and 40 keV. The measured focus size was 105 nm for a linear lens with an intensity gain of about 407, and 300 x 770 nm for a crossed lens with an intensity gain of 6470.

The nanotomography endstation at the PETRA III Imaging Beamline

The Imaging Beamline (IBL) operated by the Helmholtz-Zentrum Geesthacht (HZG) at the newly refurbished DESY PETRA III storage ring is dedicated to radiography and tomography and provides two experimental endstations, one for micro tomography and one for nano tomography. The technical specifications aim for 3D imaging with a spatial resolution of below 100 nm. This nanometer resolution will be achieved by using different combinations of compound refractive lenses as X-ray optics. In addition, a microscopic optic for magnifying the images after the converting in visible light will be used, too. The overall setup is designed to be very flexible, which allows also the implementation of other optical elements (e.g. Fresnel zoneplates, KB mirrors) as well as the application of different magnifying techniques like cone-beam tomography or X-ray microscopy. The accessible energy range for the nano tomography is 10 ? 30 keV but the beamline is designed for an energy range of 5 ? 50 keV and we aim to allow the same energy range for the nano tomography in the long run.

Submicron focusing of high-energy x-rays with Ni refractive lenses

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.

X-ray lens with kinoform refractive profile created by x-ray lithography

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.

X-ray full field microscopy at 30 KeV

In our X-ray full field microscopy experiments, we demonstrated a resolution better than 260 nm over the entire field of view of 80 μm × 80 μm at 30 keV. Our experimental setup at PETRA III, P05, had a length of about 5 m consisting of an illumination optics, an imaging lens and a detector. For imaging, we used a compound refractive lens (CLR) consisting of mr-L negative photo resist, which was fabricated by deep X-ray lithography. As illumination optics, we choose a refractive rolled X-ray prism lens, which was adapted to the numerical aperture of the imaging lens.

X-ray prism lenses with large apertures

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.

X-ray Lenses Fabricated by LIGA Technology

X-ray refractive optical lens systems have been successfully elaborated, designed, fabricated at the Institute for Microstructure Technology at the Forschungszentrum Karlsruhe (Germany) using LIGA technology in recent years. The lenses are structured in a SU-8 polymer. The capability of the LIGA technique to create an arbitrary profile of the focusing microstructures allow the fabrication of lenses with different curvature radius of parabolic geometry, minimized absorption and a large depth of focus. Also a set of planar lens systems on one substrate can be realized with 17 lenses providing identical focal distances for different X-ray energies from 2 to over 100 keV. Nickel lenses fabricated by electroforming using polymer templates can be applied for energies larger than 80 keV. The parabolic crossed lenses are used for 2D nano focusing of monochromatic beams. The quasi-parabolic crossed lenses with a submicron focus and a focus depth of the centimetre range can be used as an achromatic system. Mosaic truncated parabolic lenses with a focusing aperture up to 1 mm are made to increase the X-ray intensity in the focused spot.

A desktop X-ray monochromator for synchrotron radiation based on refraction in mosaic prism lenses

Focusing planar refractive mosaic lenses based on triangular prism microstructures have been used as an alternative approach for wide-bandpass monochromatization of high-energy X-rays. The strong energy dependence of the refractive index of the lens material leads to an analogous energy dependence of the focal length of the lens. The refractive mosaic lens, in comparison with the refractive lens of continuous parabolic profile, is characterized by a higher aperture because of reduced passive material. In combination with a well defined pinhole aperture in the focal plane, the transmittance of photons of an appropriate energy can be relatively high and photons of deviating energy can be efficiently suppressed. The photon energy can be tuned by translating the pinhole along the optical axis, and the bandwidth changed by selecting appropriate pinhole aperture and beam stop. This method of monochromatization was realised at the ANKA FLUO beamline using a mosaic lens together with a 20 µm pinhole and beam stop. An energy resolution of 2.0% at 16 keV has been achieved.

Near-diffraction limited coherent x-ray focusing using planar refractive lenses made of epoxy SU-8 resist

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.