Omnidirectional, broadband light absorption using large-area, ultrathin lossy metallic film coatings

TLDR

Resonant absorbers made from nanostructured materials promise applications in optical filtering, thermophotovoltaics, thermal emission, and hot‑electron collection, yet their industrial use is limited by costly lithographic patterning. This work demonstrates lithography‑free, broadband, polarization‑independent optical absorbers fabricated as a three‑layer ultrathin film of sub‑wavelength chromium and oxide coatings. The absorbers form an asymmetric highly‑lossy Fabry‑Perot cavity, enabling near‑perfect absorption across the visible spectrum without the need for nanostructuring. Measured absorption reaches 99.5 % from 400–800 nm, remains near‑ideal over ±60° incidence, and outperforms nanostructured plasmonic absorbers in bandwidth, polarization, and angle independence while being ultrathin and lithography‑free.

Abstract

Abstract Resonant absorbers based on nanostructured materials are promising for variety of applications including optical filters, thermophotovoltaics, thermal emitters and hot-electron collection. One of the significant challenges for such micro/nanoscale featured medium or surface, however, is costly lithographic processes for structural patterning which restricted from industrial production of complex designs. Here, we demonstrate lithography-free, broadband, polarization-independent optical absorbers based on a three-layer ultrathin film composed of subwavelength chromium (Cr) and oxide film coatings. We have measured almost perfect absorption as high as 99.5% across the entire visible regime and beyond (400–800 nm). In addition to near-ideal absorption, our absorbers exhibit omnidirectional independence for incidence angle over ±60 degrees. Broadband absorbers introduced in this study perform better than nanostructured plasmonic absorber counterparts in terms of bandwidth, polarization and angle independence. Improvements of such “blackbody” samples based on uniform thin-film coatings is attributed to extremely low quality factor of asymmetric highly-lossy Fabry-Perot cavities. Such broadband absorber designs are ultrathin compared to carbon nanotube based black materials and does not require lithographic processes. This demonstration redirects the broadband super absorber design to extreme simplicity, higher performance and cost effective manufacturing convenience for practical industrial production.