Til Florian Gunzler

Nanofocusing parabolic refractive X-ray lenses

Parabolic refractive x-ray lenses with short focal distance can generate intensive hard x-ray microbeams with lateral extensions in the 100 nm range even at a short distance from a synchrotron radiation source. We have fabricated planar parabolic lenses made of silicon that have a focal distance in the range of a few millimeters at hard x-ray energies. In a crossed geometry, two lenses were used to generate a microbeam with a lateral size of 380 nm by 210 nm at 25 keV in a distance of 42 m from the synchrotron radiation source. Using diamond as the lens material, microbeams with a lateral size down to 20 nm and below are conceivable in the energy range from 10 to 100 keV.

Refractive x-ray lenses

Parabolic refractive x-ray lenses are novel optical components for the hard x-ray range from about 5 keV to about 120 keV. They are compact, robust, and easy to align and to operate. They can be used like glass lenses are used for visible light, the main difference being that the numerical aperture is much smaller than 1 (of the order of 10−4–10−3). They have been developed at Aachen University and are made of beryllium, boron, aluminium and silicon. Their main applications are in micro- and nanofocusing, in imaging by absorption and phase contrast. In combination with tomography they allow for three-dimensional imaging of opaque media with sub-micrometre resolution. Finally, they can be used in speckle spectroscopy by means of coherent x-ray scattering. References to a number of applications are given.

Mapping the chemical states of an element inside a sample using tomographic x-ray absorption spectroscopy

Hard x-ray absorption spectroscopy is combined with scanning microtomography to reconstruct full near-edge spectra of an elemental species at each location on an arbitrary virtual section through a sample. These spectra reveal the local concentrations of different chemical compounds of the absorbing element inside the sample and give insight into the oxidation state, the local atomic structure, and the local projected free density of states. The method is implemented by combining a quick scanning monochromator and data acquisition system with a scanning microprobe setup based on refractive x-ray lenses.

Nanotomography based on hard x-ray microscopy with refractive lenses

Based on parabolic refractive x-ray lenses we have built a hard x-ray microscope that allows one to image the interior of opaque samples with submicrometer resolution. We have combined magnified imaging with tomography to obtain the three-dimensional structure of the sample at a resolution well below 1 μm. Using an aluminum lens to record a magnified tomogram of a test sample (microprocessor), a resolution of slightly above 400 nm was found for the three-dimensional reconstruction. Lenses made of beryllium are expected to improve this resolution to well below 100 nm. The resulting challenges concerning instrumentation and numerical methods are discussed.

Parabolic refractive X-ray lenses

Parabolic refractive X-ray lenses are optical components, especially suitable for third-generation synchrotron radiation sources. This article describes the status of the development of our lenses and illustrates the possibilities for micrometre and submicrometre focusing and for X-ray imaging in absorption and phase contrast. The parabolic lens profile ensures distortion-free imaging of high quality. First characteristics of Be lenses are given. A microscope based on Be lenses is expected to have a lateral resolution below 80 nm.

Parabolic refractive X-ray lenses: a breakthrough in X-ray optics

Refractive X-ray lenses, considered for a long time as unfeasible, have been realized with a rotational parabolic profile at our institute: The main features of the new lenses are: they focus in two directions and are free of spherical aberration. By varying the number of individual lenses in the stack the focal length can be chosen in a typical range from 0.5 to 2 m for photon energies between about 6 and 60 keV. The aperture of the lens is about 1 mm matching the angular divergence of undulator beams at 3d generation synchrotron radiation sources. They cope without problems with the heat load from the white beam of an undulator. Finally, they are easy to align and to operate. Refractive X-ray lenses can be used with hard X-rays in the same way as glass lenses can be used for visible light, if it is taken into account that the numerical aperture is small (of the order 10 � 4 ). Being high-quality optical elements, the refractive X-ray lenses can be used for generating a focal spot in the mm range with a gain of a factor 1000 and more, or for imaging purposes as in a hard X-ray microscope. Recent examples from microanalysis, microtomography, fluorescence tomography, X-ray microscopy will be shown to demonstrate the state of the art. Possible new developments will be discussed. # 2001 Elsevier Science B.V. All rights reserved. PACS: 41.50; 07.85.T

Beryllium parabolic refractive x-ray lenses

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.

High resolution imaging and lithography with hard x rays using parabolic compound refractive lenses

Parabolic compound refractive lenses are high quality optical components for hard x rays. They are particularly suited for full field imaging, with applications in microscopy and x-ray lithography. Taking advantage of the large penetration depth of hard x rays, the interior of opaque samples can be imaged with submicrometer resolution. To obtain the three-dimensional structure of a sample, microscopy is combined with tomographic techniques. In a first hard x-ray lithography experiment, parabolic compound refractive lenses have been used to project the reduced image of a lithography mask onto a resist. Future developments are discussed.

Hard X-ray full field microscopy and magnifying microtomography using compound refractive lenses

For hard X-rays, parabolic compound refractive lenses (PCRLs) are genuine imaging devices like glass lenses for visible light. Based on these new lenses, a hard X-ray full field microscope has been constructed that is ideally suited to image the interior of opaque samples with a minimum of sample preparation. As a result of a large depth of field, CRL micrographs are sharp projection images of most samples. To obtain 3D information about a sample, tomographic techniques are combined with magnified imaging. # 2001 Elsevier Science B.V. All rights reserved. PACS: 07.85.T; 41.50

Compact x-ray microtomography system for element mapping and absorption imaging

We have designed and built a compact x-ray microtomography system to perform element mapping and absorption imaging by exploiting scanning fluorescence tomography and full-field transmission microtomography, respectively. It is based on a low power microfocus tube and is potentially appropriate for x-ray diagnostics in space. Full-field transmission tomography yields the three-dimensional inner structure of an object. Fluorescence microtomography provides the element distribution on a virtual section through the sample. Both techniques can be combined for appropriate samples. Microradiography as well as fluorescence mapping are also possible. For fluorescence microtomography a small and intensive microbeam is required. It is generated using a polycapillary optic. Operating the microfocus tube with a molybdenum target at 12 W, a microbeam with a full width at half maximum lateral extension of 16 microm and a flux of about 10(8) photonss is generated. As an example of application, this beam is used to determine the element distribution inside dried plant samples. For full-field scanning tomography, the x-ray optic is removed and the sample is imaged in magnifying projection onto a two-dimensional position sensitive detector. Depending on the sample size, a spatial resolution down to about 10 microm is possible in this mode. The method is demonstrated by three-dimensional imaging of a rat humerus.