Efficient Third-Harmonic Generation and the Strain Engineering Control of Polarization Anisotropy in TiS₃

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 TiS₃ 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% a-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 TiS₃, 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.