AI 中文总结
该研究通过实验观测双轴范德华晶体的光谱各向异性跃迁辐射，建立薄膜跃迁辐射模型重现实验结果，证实跃迁辐射可灵敏探测双轴介质的轴依赖介电响应，为相关领域提供新自由度。
AI 中文摘要
在各向异性光学介质中，电磁响应取决于光场相对于材料主介电轴的取向，这种方向依赖性在传统光学中已被充分理解，但它也应影响自由电子驱动的光产生过程。本文通过实验观测到双轴范德华晶体产生的光谱各向异性跃迁辐射，利用硫化锗（GeS）和二氧二氯化钼（MoOCl₂）晶体的阴极发光光谱，证实跃迁辐射光谱沿面内主光学轴存在差异。为描述该光谱各向异性，本文建立了薄膜跃迁辐射模型，重现了实验观测结果。研究表明，跃迁辐射是探测双轴光学介质轴依赖介电响应的灵敏探针，且光学各向异性可为自由电子驱动的光谱学、辐射源及基于跃迁辐射的诊断提供额外自由度。
英文摘要
In anisotropic optical media, the electromagnetic response depends on the orientation of the optical field relative to the material's principal dielectric axes. While this direction dependence is well understood in conventional optics, it should also influence light-generation processes driven by free electrons. Here, we experimentally observe spectrally anisotropic transition radiation from biaxial van der Waals crystals. Using cathodoluminescence spectroscopy on germanium sulphide (GeS) and molybdenum oxydichloride (MoOCl$_2$) crystals, we show that the transition-radiation spectra differ along the principal in-plane optical axes. To describe this spectral anisotropy, we develop a thin-film transition-radiation model that reproduces the experimental observations. Our results demonstrate that transition radiation is a sensitive probe of the axis-dependent dielectric response of biaxial optical media and suggest that optical anisotropy can provide an additional degree of freedom for free electron-driven spectroscopy, radiation sources, and transition-radiation-based diagnostics.
