Reflection analysis of absorbing film with diffractive structures for incoherent light by rigorous coupled-wave...

Reflectivity is useful for evaluating the extinction coefficient; however, it is highly sensitive to the refractive index structure. In this study, we propose a novel, to the best of our knowledge, method for evaluating the influence of the structure on reflectivity using rigorous coupled-wave analysis (RCWA), and apply it to analyze the reflectivity of the dye rhodamine B. The reflection-absorption spectrum of the film was significantly affected by its surface and internal structure. We found that simulating the reflectivity of a film with an unknown internal structure, using the coherency parameter is convenient. The RCWA facilitated simultaneous treatment of the coherent diffraction by the surface structure and incoherent reflection in the film.