X-ray propagation in tapered waveguides: Simulation and optimization

We use the parabolic wave equation to study the propagation of X-rays in tapered waveguides by numerical simulation and optimization. The goal of the study is to elucidate how beam concentration can be best achieved in X-ray optical nanostructures. Such optimized waveguides can e.g. be used to investigate single biomolecules. Here, we compare tapering geometries, which can be parametrized by linear and third-order (Bézier-type) functions and can be fabricated using standard e-beam lithography units. These geometries can be described in two and four-dimensional parameter spaces, respectively. In both geometries, we observe a rugged structure of the optimization problem’s “gain landscape”. Thus, the optimization of X-ray nanostructures in general will be a highly nontrivial optimization problem.