径向偏振高次方指数涡旋光束的紧聚焦特性

Tight focusing of radially polarized power-exponent-phase vortex beam

摘要:

为了获得一些具有特殊光强分布的波长量级聚焦 光斑,理论研究了具有径 向偏振特性的高次方涡旋光束经过大数值孔径透镜的聚焦。基于矢量德拜理论,对 径向偏振高次方涡旋光束经过大数值孔径透镜聚焦的光强和相位进行了数值模拟 研究。关于聚焦平面光强分布的研究发现,聚焦光斑的光强与高次方涡旋光束的拓 扑荷数和幂次方数有关。拓扑荷数为1的一次方涡旋光束的聚焦光强呈现圆对称分 布,随着光束幂次方数的增加,演变为非圆对称分布。拓扑荷数为2的一次方涡旋 光束的聚焦光斑为中空的圆对称分布,随着光束幂次方数的增加,其暗核形状会变 化并最终消失。紧聚焦的径向偏振光会产生较强的纵向分量,因此本文还研究了光 束的纵向相位分布,研究发现纵向相位奇点的数目与涡旋光束的拓扑荷数相同。获 得了不同光强分布的尺寸为波长量级的聚焦光斑,这些研究结果有望在基于激光的 光学操控中得到应用。

Abstract:

In order to generate beams with size of wavelength,the property of ra dially polarized power-exponent-phase vortex beam focused by a high numerical aperture objectiv e is theoretically studied.Based on vectorial Debye theory,the intensity and phase near the focus formed by a tightly focused radially polarized power-exponent phase vortex beam is investigated by numerical simulation in detail.It is shown that the intensity d istribution depends on the topological charge and the power index of vortex beam.A focal sp ot with circular symmetry distribution is generated by vortex beam with topological char ge of 1and power index of 1,and the symmetry disappears with increase of power index.Circular focal spot with a dark core is generated by vortex beam with topological charge of 2and power ind ex of 1,and the dark core disappears gradually with increase of power index.As a tightly foc used radially polarized beam produces a strong longitudinal component,the phase of longitudin al component is investigated.It is interesting to find that the number of phase si ngularity is the same as the topological charge of vortex beam.The results show that different focal spot with size of wavelength can be generated,which may have potential applications in optical ma nipulation.