双环角向偏振光束深聚焦特性

基于Richards-Wolf矢量衍射积分公式，研究了双环角向偏振光束经环状高数值孔径透镜的聚焦特性，推导了双环角向偏振光束经环状透镜深聚焦的光强表达式。根据数值模拟结果，比较了相关参量的变化对深聚焦特性的影响。研究表明:入射光束经环状高数值孔径透镜聚焦后，在焦平面得到了具有广泛应用的亚波长空心光斑，并且入射光束的相关参数和聚焦透镜的数值孔径大小都会影响光束的聚焦特性，使聚焦空心光斑达到亚波长量级;双环角向偏振光束经环状高数值孔径透镜的聚焦以后，在焦平面附近产生了一个更长的焦深（约28倍入射光波长）。

Tight focusing properties of double-ring-shaped azimuthally polarized beam through annular high numerical aperture

By using the Richards-Wolf vector diffraction theory, the focusing properties of a double-ring-shaped azimuthally polarized beam through an annular lens with high numerical aperture are studied. Expressions of intensity distribution on the focal field are derived. Numerical calculations are performed to compare the influence of the beam and lens parameters on the tight focusing properties. It is shown that sub-wavelength focal spots of wide applications can be obtained on the focal plane, and correlated parameters of the incident beam and the numerical-aperture of the lens do affect the focusing. Moreover, longer depth of focus (nearly 28 times the incident wavelength) can be generated with a lens of higher numerical aperture.