Design methodology of broadband near-perfect thin-film absorbers based on ideal dispersion relations

We propose a theoretical framework based on ideal dispersion to achieve broadband perfect absorption in thin-film structures with alternating lossy and dielectric layers. Using the Airy formula, the ideal dispersion relation of the lossy material required for perfect absorption is analytically derived, providing explicit guidance for material selection and layer-thickness design. Thin-film absorbers designed and fabricated for the visible and near-infrared bands exhibit average absorptances exceeding 0.97, in agreement with theoretical predictions. This framework is extendable to other spectral ranges, offering a reliable route toward high-performance, customizable optical absorbers.