Robust high-Q perfect absorption based on guided modes in dielectric gratings

Achieving high-Q perfect absorption (PA) in plasmonic systems has long been challenging due to the intrinsic high loss of metals, which often limits the quality factor (Q-factor) of resonances. In this paper, we present a novel hybrid structure that overcomes this limitation by combining gold nanoparticles with dielectric gratings, enabling robust, high-Q, and near-perfect absorption. Our approach consists of two key design steps: (1) a highly reflective dielectric grating is optimized based on temporal coupled mode theory (TCMT) to serve as a loss-engineered background; (2) gold absorbers are strategically positioned to meet the PA condition, leveraging guided modes (GMs) in the non-resonant regions of localized surface plasmon resonance (LSPR). This dual-modality interaction achieves dual-band near-perfect absorption with Q-factors as high as 2 × 10 4 and 7 × 10 3 in the near-infrared region—setting new benchmarks for plasmonic systems. Additionally, by introducing structural symmetry to induce destructive interference, we demonstrate tunable single-band high-Q PA with a Q-factor exceeding 2 × 10 4 . These results represent the highest reported Q-factors for near-perfect absorption in plasmonic systems to date. Moreover, the structure exhibits remarkable tolerance to fabrication imperfections, underscoring its practical robustness. This work pioneers a pathway for advancing high-Q plasmonic nano-systems and opens new opportunities in precision sensing, photodetection, and the development of efficient thermal emitters.