Rigorous speckle simulator for large area rough surfaces using surface integral equations and multilevel fast multipole method

Scattering of electromagnetic waves from rough surfaces has been actively studied for more than a century, since it is involved in wide-ranging applications, among which optical metrology for surface inspection is especially interesting for us. Through analyzing the speckle fields, profound information of the surface under inspection can be retrieved. Hence, calculation of scattered near and far fields from rough surfaces is indispensable for understanding the statistical properties of speckles and for evaluating the roughness of the optical surfaces. We report a rigorous speckle simulator developed for large area rough surfaces of general materials including metals using surface integral equations and multilevel fast multipole method (MLFMM) implemented using Fortran 2003. The surface under study is meshed using two methods: higher order 8-node quadrilateral elements and flat triangular rooftop elements. Via MLFMM, the computation cost is reduced from O(N2) to O(NlogN). Calculation results with full field information including polarization from both measured and numerically generated rough surfaces with a size of 1x1 mm2 will be reported.