Abstract: A method for modeling optical scattering includes an initial step of defining a zero-th order structure (an idealized representation) for a subject including a perturbation domain and a background material. A Green's function and a zero-th order wave function are obtained for the zero-th order structure using rigorous coupled wave analysis (RCWA). A Lippmann-Schwinger equation is constructed including the Green's function, zero-th order wave function and a perturbation function. The Lippmann-Schwinger equation is then evaluated over a selected set of mesh points within the perturbation domain. The resulting linear equations are solved to compute one or more reflection coefficients for the subject.