Complex Refraction Metasurfaces for Locally Enhanced Propagation Through Opaque Media

Metasurfaces with linear phase gradients can redirect light beams. Controlling both phase and amplitude of a metasurface is proposed to extend Snell's law to the realm of complex angles, enabling a non-decaying transmission through opaque media with complex refractive indices. This leads to the discovery of non-diffracting and non-decaying solutions to the wave equation in opaque media, in the form of generalized cosine and Bessel-beams with a complex argument. While these solutions present nonphysical exponentially growing side tails, this is addressed via a windowing process, removing the side tails of the field profile while preserving significant transmission enhancement through an opaque slab on a small localized region. Such refined beam profiles may be synthesized by passive metasurfaces with phase and amplitude control at the opaque material's interface. The findings, derived from rigorous solutions of the wave equation, promise new insights and enhanced control of light propagation in opaque media. This paper introduces complex refraction metasurfaces, utilizing phase and amplitude control to extend Snell's law to complex angles, and enabling non-decaying wave solutions in opaque media. The study addresses nonphysical growing side tails using a windowing process, resulting in 'bullseye' metasurfaces that achieve significant light transmission through opaque slabs in localized regions, with potential applications in medicine and communications.image