Influence of spatial dispersion in metals on the optical response of deeply subwavelength slit arrays

In the framework of the hydrodynamic model describing the response of electrons in a metal, we show that arrays of very narrow and shallow metallic slits have an optical response that is influenced by the spatial dispersion in metals arising from the repulsive interaction between electrons. As a simple Fabry-Perot model is not accurate enough to describe the structure's behavior, we propose to consider the slits as generalized cavities with two modes, one being propagative and the other evanescent. This very general model allows to conclude that the impact of spatial dispersion on the propagative mode is the key factor explaining why the whole structure is sensitive to spatial dispersion. As the fabrication of such structures with relatively large gaps compared to previous experiments is within our reach, this work paves the way for future much needed experiments on nonlocality.