Longitudinal electromagnetic fields generally become comparable with the usually dominant transverse components in strongly focused, non-paraxial beams. For paraxial optical vortex modes it is highlighted here how their angular momentum properties produce longitudinal fields that in general must be accounted for. First-order longitudinal components of quantized Laguerre–Gaussian modes are derived and numerically studied with respect to the paraxial parameter, highlighting light-matter and spin-orbit interactions that stem from the longitudinal fields of paraxial beams in free space. New restrictions are cast on the validity of neglecting longitudinal fields for paraxial optical vortices interacting with atoms, molecules and other nanostructures.

纵向电磁场通常与强聚焦的非近轴光束中通常占主导地位的横向分量相当。对于近轴光学涡流模式，这里强调了它们的角动量特性如何产生通常必须考虑的纵向场。推导出量化拉盖尔-高斯模式的一阶纵向分量，并就近轴参数进行数值研究，突出了源自自由空间中近轴光束纵向场的光-物质和自旋-轨道相互作用。对忽略与原子、分子和其他纳米结构相互作用的近轴光学涡旋的纵向场的有效性施加了新的限制。