High-efficiency Bragg-Fresnel lenses with 100 nm outermost zone width

In this article, we describe the manufacture and characterization of linear silicon Bragg-Fresnel lenses (BFLs) with outermost zone widths of 100 nm. This is, to our knowledge, a factor of 3 smaller than any other device of this kind reported so far. Furthermore, we give the first detailed description of an accurate and robust method to measure the diffraction efficiency of BFLs. The first-order diffraction efficiency of our lenses at 13.25 keV photon energy was 26%+/- 0.5%. The combination of wide aperture angle, high efficiency, and large size of our devices results in a significant gain in achievable x-ray flux. (C) 1999 American Institute of Physics. [S0034-6748(99)05111-4].