Focusing geometry.
To generate a small x-ray beam, the x-ray source is imaged onto the sample position in a strongly reducing geometry. This requires the focal length f of the optic to be small compared to the source-to-optic distance L1.
Nanofocusing lenses are capable of focusing hard x-rays with focal distances f in the range of one centimeter. Since these short focal distances require extremely small radii of curvature R, these lenses are made by nanofabrication techniques, i. e., by electron beam lithography and subsequent deep reactive ion etching.
Nanocusing X-Ray Lenses.
The Figure shows a scanning electron micrograph of a series of nanofocusing lenses placed next to each other. Each of them is made of a large number N of single lenses that have parabolic shape. Since these optics are curved only in one direction, they generate a line focus. Two such lenses need to be aligned behind each other in crossed geometry to generate a point focus. With these lenses, a focus of 47 by 55 nm was generated for 21 keV x-rays.
