Refractive X-ray beam shaping

This work introduces new refractive illumination optics in the hard X-ray region and describes a method for overcoming fabrication limitations of X-ray depth lithography. In particular, the problem of high aspect ratio in X-ray prism lenses was addressed. The refractive X-ray optics are developed for the photon energy range 8-100 keV. In the following, we report the development of a principal new focusing optics with large aperture, an illumination condenser for full-field X-ray microscopy and a so-called beam shaping optics to overcome the limitation of the field of view at 3rd and 4th generation synchrotron sources. To reduce the absorption of X-rays in the material of the optical systems, the approach of X-ray prism lenses was pursued. Here, the optics consist of rows of micro prisms with an edge length of about 20 µm, which deflect the incident rays. This improves the ratio of the refractive power of the optics to the volume of the absorbing lens material. The mechanical stability of the fragile, very tall micro prisms is achieved by exposing thin, stabilizing support planes. In order to achieve focal sizes smaller than the prism edge lengths, double parabolic biconcave micro-lenses were added to the prism rows. A similar arrangement with biconvex micro-lenses was used to achieve beam expansion while simultaneously homogenizing the illumination of the image field of a full-field X-ray microscope. Beam shaping optics consisting of kinoform Fresnel lens elements were developed for vertical beam expansion at high brilliance synchrotron sources. In all cases, the theory is based on geometrical optics and ray tracing simulations. The optics were produced via deep X-ray lithography using the synchrotron radiation source at KIT at the LIGA I and II beamlines. The lens material is the negative resist mr-X, an epoxy resin-based polymer of type SU-8. The lenses were characterized at PETRA III, DESY in Hamburg and at ESRF in Grenoble