Examining and explaining the "generalized laws of reflection and refraction" at metasurface gratings

The widespread concept of "generalized laws of reflection and refraction" that is commonly applied to wave propagation through metasurfaces is thoroughly explained on the foundation of diffraction theory. This allows definition of strict constraints to the applicability of these generalized laws and highlights the underlying physical effects. A diffraction-based explanation of the reported phenomena is provided that yields a solid theoretical foundation for the prediction of experimental results and that clarifies many of the convoluted explanations found throughout the literature.