Broadband perfect absorption of ultrathin conductive films with coherent illumination: Superabsorption of microwave radiation

Absorption of microwaves by metallic conductors is typically inefficient, albeit naturally broadband, due to the huge impedance mismatch between metal and free space. Reducing metal to ultrathin profile may improve absorption efficiency, but a maximal 50% absorption limit induced by the field continuity exists. Here, we experimentally show that broadband, perfect (100%) absorption of microwaves can be realized in a single layer of ultrathin conductive film when illuminated coherently by two oppositely directed incident beams. Our experiments keep the field continuity and simultaneously break the 50% limit. Inheriting the intrinsic broadband feature of metals, complete absorption is observed to be frequency independent in microwave experiments from 6 to 18 GHz. Remarkably, this occurs in films with thicknesses that are at the extreme subwavelength scales, similar to lambda/10000 or less. Our work proposes a way to achieve total electromagnetic wave absorption in an ultrawide spectrum of radio waves and microwaves with a simple conductive film.