LAUSR

We demonstrate through numerical experiments and analytical calculations that extreme subwavelength gaps between two corrugated surfaces support high effective refractive index guided modes. The corrugated gap mode is of low loss because it does not rely on plasmonic currents induced inside a metal. This enables guided modes with a much higher effective refractive index than is possible in natural plasmonic materials. These high-index guided modes are incorporated as periodic slots in an opaque screen, which is then shown to support broadband highly transmitting modes at a certain oblique incidence angle in addition to the usual Fabry–Perot resonances. This anomalously high transmission is the extension of the plasmonic Brewster angle to arbitrarily low frequency, controlled by the geometry of the corrugated slots. We demonstrate the preservation of the shape of a broadband low-frequency pulse transmitted through the slotted screen, opening up the possibility to use the structure for broadband energy squeezing applications in the GHz to THz regime.