Zoneplates for hard X-rays with ultra-high diffraction efficiencies

We report on the fabrication and testing of linear multilevel zone plates made of silicon. The lenses were tilted with respect to the x-ray beam, enabling an increase of the effective height of the diffractive structures in order to obtain optimal efficiency of these devices even for high photon energies. We achieved unprecedented diffraction efficiencies between 64 and 67% (between 47 and 59% considering membrane absorption) for photon energies between 10 and 15 keV. As a linear zone plate acts as a cylindrical lens, two perpendicular lenses have to be put in series to obtain a 2-D focusing. The resulting micro-focusing device has a very high total efficiency (approx. 30%) and can be matched to the asymmetry of synchrotron in order to obtain a symmetric micro-focus.