A Monte Carlo approach for simulating the propagation of partially coherent x-ray beams

Advances at SR sources in the generation of nanofocused beams with a high degree of transverse coherence call for effective techniques to simulate the propagation of partially coherent X-ray beams through complex optical systems in order to characterize how coherence properties such as the mutual coherence function (MCF) are propagated to the exit plane.

Here we present an approach based on Monte Carlo sampling of the Green function. A Gauss-Shell Stochastic Source with arbitrary spatial coherence is synthesized by means of the Gaussian copula statistical tool. The Green function is obtained by sampling Huygens-Fresnel waves with Monte Carlo methods and is used to propagate each source realization to the detector plane.

The sampling is implemented with a modified Monte Carlo ray tracing scheme where the optical path of each generated ray is stored. Such information is then used in the summation of the generated rays at the observation plane to account for coherence properties. This approach is used to simulate simple models of propagation in free space and with reflective and refractive optics.