Computer simulations and experimental results on air-gap X-ray waveguides

X-ray Waveguides (WG) are optical elements able to provide nanometer size coherent X-ray beams. Both Resonant beam Coupling (RBC) and Front Coupling (FC) can be implemented to couple the incident radiation with the WG. In this paper we implemented a computer code based on finite difference scheme solutions of parabolic wave equations to simulate the coupling and the propagation of electromagnetic waves into air-gap waveguides in Front Coupling mode. Both a synchrotron source and a table-top laboratory sources have been considered. In this last case the degree of coherence of the incoming beam has been explicitly taken into consideration. Air-gap WGs have been fabricated following simple procedures, and tested at the Elettra synchrotron source. The results are in good agreement with theoretical expectations.