Focus characterization of a Beryllium CRL by ptychographic imaging

The nanoprobe endstation at PETRA III P06 [1] provides the possibility to change the optics unit in the scanner frame shown in Figure 1(b). This feature allows one to study and characterize all kind of different nanofocusing optics such as FZPs, MLLs, NFLs, and CRLs. The latter were used in this experiment to demonstrate the feasibility of coherent imaging techniques using this kind of optic. We used 36 single lenses made of beryllium with a biconcave shape, a radius of curvature R at the apex of a lens of R = 50μm, and a housing thickness of W = 2mm. Combining these we build a 72mm thick lens with a nominal focal length of f = 143.2mm for the used photon energy of E = 8.0 keV (λ = 1.55 Å). The maximum geometrical aperture of the lens is given by the thickness of the beryllium foils used. With a thickness of l = 1mm, the aperture Dgeo is given with 440μm. Further experiments in late 2010 showed, that small-angle scattering in the lens is an issue for coherent imaging techniques. To resolve this problem we only illuminated the inner part of the CRL using a double slit system in front of them as depicted in Figure 1(a). For an initial experiment we used a slit opening of 80 × 80μm, reducing the geometrical aperture Dgeo. This results in a smaller numerical aperture NA, which is half of the opening angle of the optic and for small angles given as NA = Dgeo/(2f), and thus a larger size dt of the diffraction limited beam.