Nonlinear optical activities, especially second harmonic generation (SHG), are key phenomena in inversion-symmetry-broken two-dimensional (2D) transition metal dichalcogenides (TMDCs). On the other hand, anisotropic nonlinear optical processes are important for unique applications in nano-nonlinear photonic devices with polarization functions, having become one of focused research topics in the field of nonlinear photonics. However, the strong nonlinearity and strong optical anisotropy do not exist simultaneously in common 2D materials. Here, we demonstrate strong second-order and third-order susceptibilities of 64 pm/V and 6.2×10⁻¹⁹ m²/V², respectively, in the even-layer PdPSe, which has not been discovered in other common TMDCs (e.g., MoS₂). Strikingly, it also simultaneously exhibited strong SHG anisotropy with an anisotropic ratio of ~45, which is the largest reported among all 2D materials to date, to the best of our knowledge. In addition, the SHG anisotropy ratio can be harnessed from 0.12 to 45 (375 times) by varying the excitation wavelength due to the dispersion of \({\chi }^{(2)}\) values. As an illustrative example, we further demonstrate polarized SHG imaging for potential applications in crystal orientation identification and polarization-dependent spatial encoding. These findings in 2D PdPSe are promising for nonlinear nanophotonic and optoelectronic applications.

非线性光学活动，特别是二次谐波产生（SHG），是反演对称破缺二维（2D）过渡金属二硫属化物（TMDC）中的关键现象。另一方面，各向异性非线性光学过程对于具有偏振功能的纳米非线性光子器件的独特应用具有重要意义，已成为非线性光子学领域的重点研究课题之一。然而，强非线性和强光学各向异性在常见的二维材料中并不同时存在。在这里，我们在偶数层 PdPSe 中分别展示了 64 pm/V 和 6.2×10 ^-19 m ² /V ²的强二阶和三阶磁化率，这在其他常见 TMDC 中尚未发现（例如，MoS ₂ ）。引人注目的是，它还同时表现出强大的二次谐波各向异性，各向异性比约为 45，据我们所知，这是迄今为止所有二维材料中报道的最大的。此外，由于\({\chi }^{(2)}\)值的色散，通过改变激发波长，可以将 SHG 各向异性比从 0.12 调整到 45（375 倍）。作为一个说明性的例子，我们进一步证明了偏振倍频成像在晶体取向识别和偏振相关空间编码中的潜在应用。二维 PdPSe 的这些发现对于非线性纳米光子和光电应用来说是有希望的。