Multimode coupled titanium-based multi-level nested cavity broadband solar absorber

To address the demand for broadband, high-temperature stable, and wide-angle polarization compatible photothermal devices in scenarios such as centralized solar thermal power generation, thermophotovoltaics, and high-temperature infrared radiation sources, this paper designs a Ti/SiO₂ beacon-shaped multi-level nested cavity broadband solar absorber. This structure consists of a bottom Ti substrate, a bottom SiO₂ dielectric layer, a Ti trapezoidal frustum, intermediate insulating SiO₂ layers, and a top Ti square cavity stacked layer by layer. Full-band optical simulation was performed using FDTD. Spectroscopic results show that the device maintains a stable absorptivity above 90% in the 280-4833 nm range, with an average absorptivity of 97.65%, and a solar energy capture efficiency of 98.3% obtained by standard solar spectrum integration. Three characteristic resonance peaks at 599 nm, 1896 nm, and 3435 nm were selected to reveal the physical mechanism through electromagnetic field analysis. Parameter discussions were conducted systematically to explore the control law of geometric dimensions on the absorption bandwidth and determine the optimal structural parameters. High-temperature thermal radiation simulations demonstrate that the device maintains a radiation efficiency above 95% in the 500-2000 K range, perfectly conforming to Kirchhoff's thermal radiation law. TE/TM polarization isohyets with oblique incidence at 0°-60° confirm that the device possesses polarization-independent, wide-angle stable absorption characteristics. The multi-level nested refractory metal-dielectric resonant structure proposed in this paper achieves ultra-wide spectrum high-efficiency light capture through multi-mode coupling of multi-order FP cavities, LSPR, and magnetic dipole resonance. It also has the advantages of high temperature stability, polarization insensitivity and wide-angle adaptability, providing a theoretical basis and optimization scheme for the design of high-temperature broadband solar photothermal absorption-emission integrated devices.