Anisotropic Second‐ and Third‐Harmonic Hermite–Gaussian Beam Generation with NbOI₂ Holograms

Hermite–Gaussian (HG) modes are an orthogonal set of solutions to the paraxial wave equation possessing distinct spatial intensity variations, which are important in many optical applications. Here, anisotropic second‐ and third‐harmonic HG beam generation is demonstrated with ultrathin niobium oxide diiodide (NbOI 2 ) grating holograms to produce the nonlinear HG 01 and HG 10 modes. It is shown that the generated second‐harmonic HG modes exhibit a high anisotropy ratio reaching a large value of 14.95, while the simultaneously generated third‐harmonic HG modes have an anisotropy ratio up to 4.85. The relative magnitudes of the second‐ and third‐order nonlinear susceptibility tensor elements of NbOI 2 crystal are extracted by analyzing the polarization‐dependent nonlinear emission. These demonstrations provide new opportunities for building functional polarization‐sensitive nonlinear optical devices used for future integrated photonic chips, optical computing, and optical communication.