which is described in works of Stearns:
Spiller__Stearns__Krumrey_-1993-_Multilayer_x_ray_mirrors_Interfacial_roughness__scattering__and_image_quality.pdf
Stearns_-1993-_Stochastic_model_for_thin_film_growth_and_erosion.pdf
Stearns_et_al._-1998-_Nonspecular_x-ray_scattering_in_a_multilayer-coated_imaging_system.pdf
Stearns__Gullikson_-2000-_Nonspecular_scattering_from_extreme_ultraviolet_multilayer_coatings.pdf