非对称离轴双相位奇点高斯光束的强聚焦特性

Tight Focusing Properties of Gaussian Beams with Asymmetric Off-Axis Bi-Phase Singularities

涡旋光束的中心为相位奇点,通常涡旋光束的涡旋轴(即相位奇点)位于光束的光轴上。但是考虑误差的存在,实际生成的涡旋光束会存在一定程度的离轴,因此研究离轴的相位奇点光束的特性具有重要的应用价值。基于RichardsWolf矢量衍射理论,研究了具有非对称离轴双相位奇点的径向偏振高斯光束经过大数值孔径透镜后的强聚焦特性,主要分析了离轴距离和涡旋拓扑荷数对聚焦场的影响。研究结果表明:两个离轴距离和对应的两个拓扑荷数的相对大小对聚焦场光强的最大值偏移方向的影响是一致的;高阶涡旋光束的聚焦场会发生暗核分裂现象,出现多个暗核,暗核的个数等于两个涡旋拓扑荷数的相加值再减1。

The center of a vortex beam is a phase singularity,and in general,the vortex axis(i.e.,the phase singularity)of the vortex beam is on the optical axis of the beam.Due to consideration errors,however,a generated vortex beam is offaxis to some extent,and therefore,it is of great application value to investigate the characteristics of beams with off-axis phase singularities.In this paper,the tight focusing properties of radially polarized Gaussian beams with asymmetric offaxis bi-phase singularities upon passing through a lens with a large numerical aperture are investigated on the basis of the Richards-Wolf vector diffraction theory.In particular,the influences of off-axis distance and the vortex topological charge number on the focusing field are analyzed.The results reveal that the relative quantities of two off-axis distances and the corresponding two topological charge numbers have a consistent influence on the offset direction of the maximum light intensity of the focusing field.In addition,it is found that dark core splitting occurs in the focusing field of high-order vortex beams.Thus,multiple dark cores appear,and the number of dark cores is equal to the sum of two vortex topological charge numbers subtracted by 1.