Achieving multi-order nearly perfect absorption based on phase resonance in a compound metallic grating

In this study, a free-standing subwavelength metallic grating with grooves on its output surface is shown to have suppressed transmission and reflection simultaneously at different incident wavelengths both for normal incidence and oblique incidence, resulting in multi-order nearly perfect absorption. This extraordinary absorption originates from the phase resonance of this compound grating together with the contribution of the cavity modes (CMs) resonance in the grating slits. The CMs resonance gives rise to the suppressed reflection, and the phase resonance not only reinforces this suppression effect, but also blocks the transmission completely. Compared with the conventional perfect absorbers, this perfect absorber has obvious advantages, such as simple single layer structure, single material composition, can be achieved at multiple frequencies and wide angular range.