基于4Pi聚焦系统的圆柱矢量涡旋光束的焦场调控

Focal Field Modulation of Cylindrical Vector Vortex Beams Based on 4Pi Focusing System

基于Richards-Wolf矢量衍射积分理论,研究了拉盖尔-高斯分布圆柱矢量(CV)涡旋光束同轴相向入射到插入了衍射光学元件(DOE)的由两个相同高数值孔径透镜构成的4Pi聚焦系统的聚焦特性。数值模拟结果表明,DOE的相位调制使焦场呈现球形结构,增加DOE的环数可以得到更多的光球。采用六环DOE且两侧入射光束同相时,当拓扑电荷m=0,径向偏振光束聚焦得到6个半峰全宽均为0.42λ(λ为波长)并以间距0.83λ沿轴向排列的单行多光球结构;角向偏振光束聚焦得到每行各5个光球且行间距为0.75λ的双行多光球结构,其大小和纵向间距与径向聚焦结果一致;偏振角为52°的CV光束聚焦可以形成光链结构。m=±1时CV涡旋光束的聚焦也能得到光链结构;m=2时其焦场强度分布会转化为暗通道结构。此外,通过调节4Pi聚焦系统两侧入射光束的相位差还可以控制生成的焦场沿着纵向方向移动,移动距离与相位差为线性关系,且移动速度与相位差的变化速率线性相关。这些结果对于微观粒子的捕获和操控具有潜在的应用价值。

Based on Richards-Wolf vector diffraction integral theory, we investigate the focusing characteristics of Laguerre-Gaussian-distributed cylindrical vector(CV) vortex beams coaxially incident on a 4Pi focusing system. The focusing system is composed of two identical high-numerical-aperture lenses, with diffractive optical elements(DOEs)inserted. The numerical simulation results show that the phase modulation of DOE makes the focal field exhibit a spherical structure, and more optical spheres can be obtained by increasing the number of DOE rings. Applying six-ring DOE, we obtain six optical spheres arranged axially in one row at the spacing of 0.83λ(λ is wavelength) with a full width at halfmaximum(FWHM) of 0.42λ after the focusing of the radially polarized beams under the conditions of in-phase incident beams on both sides and the topological charge m = 0. The focusing of the azimuthally polarized beams under the same conditions generates a double-row structure with 5 optical spheres in each row and the row spacing of 0.75λ. In such a case, the size and longitudinal spacing are consistent with the radial focusing results. An optical chain can be formed by the focusing of CV beams with a polarization angle of 52°. The optical chain structure can also be obtained by the focusing of CV vortex beams with m = ±1. The focal field intensity distribution of the focused CV vortex beams transforms into a dark channel structure when m = 2. Furthermore, the focal field can be controlled to move in the longitudinal direction by adjusting the phase difference of the incident beams on both sides of the 4Pi focusing system. The moving distance has a linear relationship with the phase difference, and the moving speed is linearly related to the change rate of the phase difference. These results have potential applications in microparticle trapping and manipulation.