We proposed a type of tightly autofocusing beams (TABs) to create and enhance longitudinally polarized fields with subdiffraction beam sizes. It reveals that the TABs can automatically focus and behave with similar focusing properties to those with a high numerical aperture lens; a radially polarized beam generates a strong longitudinal field, while the azimuthally polarized one cannot. By reducing the order of the TAB, the maximum conversion efficiency of light to longitudinal field is as high as 98.32% in theory. As such, we demonstrate that the spin-to-orbital angular momentum conversion is also enhanced by circularly polarized TABs.

中文翻译：

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紧密自动聚焦的光束：有效增强纵向偏振场

我们提出了一种紧密自动聚焦光束（TAB），以创建和增强具有亚衍射光束尺寸的纵向偏振场。它表明TAB可以自动聚焦并表现出与高数值孔径镜头相似的聚焦特性。径向极化的光束会产生很强的纵向场，而方位极化的光束则不会。通过减小TAB的阶数，理论上光到纵向场的最大转换效率高达98.32％。这样，我们证明了圆极化TAB也增强了自旋至轨道角动量的转换。