Efficient Third-Harmonic Generation and the Strain Engineering Control of Polarization Anisotropy in TiS<sub>3</sub>.

Zhang, Shunhui; Wan, Zhenzhen; Dai, Jin; Zhang, Hua; Zhou, Yu; Zhu, Menglong; Chen, Zhihui; Ouyang, Fangping et al. · Nano Lett · 2026

basic_science · Level V

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Abstract

Strain engineering, as a key strategy for regulating two-dimensional (2D) material anisotropy, has demonstrated remarkable effectiveness in band engineering. However, systematic investigations of the third-order nonlinear-optical (NLO) response of low-symmetry materials under strain fields still pose a significant challenge. This study combines experimental and theoretical approaches to reveal for the first time the extreme sensitivity of third-harmonic generation (THG) anisotropy in quasi-one-dimensional-layered TiS<sub>3</sub> to uniaxial strain. Due to the anisotropic reconstruction of interband transition dipole moment, the THG anisotropy ratio reaches 316.90 ± 7.93 under 7.25% <i>a</i>-axis strain, which is the largest reported in 2D materials, to our best knowledge. Based on the excellent third-order nonlinear anisotropy and strain regulation characteristics of TiS<sub>3</sub>, an all-optical Boolean logic gate based on NLO intensity encoding was further constructed. This work not only elucidates the strain-NLO coupling mechanism but also proposes a tunable nonlinear all-optical device based on anisotropic 2D materials.