New design schemes for x-ray waveguides based on multiple guiding layers and two-dimensional nano-structures

Planar x-ray waveguide structures can be used as resonant beam coupling devices to produce a coherent and divergent x-ray line source with cross-sections in the sub-micrometer range. This article reviews the basic x-ray optical properties of such devices and generalizes the principle of resonant x-ray beam coupling to waveguides containing multiple guiding layers. In such a device, several coherent beams of a width on the order of 100 Angstrom to 1000 Angstrom can be extracted at the end of the waveguide. Besides coherent diffraction and imaging, interferometry with two or more nanometer sized beams can be envisioned. Furthermore this article presents measurements of the internal reflection of an excited x-ray waveguide mode in a synthetic nanostructure defined by e-beam lithography. In this device the x-ray beam is first coupled into a conventional vertical thin film waveguide structure and then reflected laterally at the quasi one-dimensional edge of the waveguiding layer. The reflectivity of the quasi one-dimensional interface has been recorded under simultaneous excitation of the (vertical) waveguide mode. This experiment constitutes an important step towards the production of a coherent, nanometer sized x-ray point source by two-dimensionally defined waveguide structures.