Broadband and efficient third-harmonic generation from black phosphorus-hybrid plasmonic metasurfaces in the mid-infrared.

Zhu, Song; Chen, Wenduo; Temel, Tugba; Wang, Fakun; Xu, Xiaodong; Duan, Ruihuan; Wu, Tingting; Mao, Xuan et al. · Sci Adv · 2025

basic_science · Level V

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Abstract

Black phosphorus (BP), with a mid-infrared (MIR) bandgap of 0.34 eV, presents itself as a promising material for MIR nonlinear optical applications. We report the realization of MIR third-harmonic generation (THG) in both BP and BP-hybrid plasmonic metasurfaces (BPM). BP exhibits a high third-order nonlinear susceptibility ([Formula: see text]) exceeding 10<sup>-18</sup> m<sup>2</sup>/V<sup>2</sup> in the MIR region with a maximum value of 1.55 × 10<sup>-17</sup> m<sup>2</sup>/V<sup>2</sup> at 5000 nm. The BP flake achieves a THG conversion efficiency of 1.4 × 10<sup>-5</sup>, surpassing that of other 2D materials by over one order of magnitude. To further enhance this nonlinear performance, a BPM is designed and fabricated to achieve a two-order-of-magnitude enhancement in THG, leading to a record conversion efficiency of 6.5 × 10<sup>-4</sup>, exceeding the performance of previously reported metasurfaces by more than one order of magnitude. These findings establish BP as a promising platform for next-generation MIR nonlinear optical devices.