Abstract We propose a simple and effective method to generate an ultra-long and high uniform optical needle through tightly focusing a radially polarized beam with a pure-phase filter modulation. An optical needle with strong longitudinally polarized field is obtained through creating, shifting and merging multifocal spots on the optical axis. Genetic algorithm is introduced to improve the optimizing efficiency and provide a universal approach for solving multifocal positions simultaneously. The axial full-width at half-maximum (FWHM) along the optical axis has been extended to 20.3 λ . More attractively, the 18 λ long central part of the needle exhibits a uniformity of 96.7%. The maximum side lobes in axial and radial directions are 2% and 23% respectively. We further explored the maximum uniform length can be achieved in the needle under various amounts of focal spots to be merged, which may provide a reference for designing a uniform optical needle with customized length. The proposed methods offer simple and effective design processes for ultra-long and high uniform optical needles, which may find wide applications in particle acceleration and optical trapping.

中文翻译：

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基于遗传算法的多焦点位置优化生成的超长高均匀光针

摘要 我们提出了一种简单有效的方法，通过用纯相位滤波器调制紧密聚焦径向偏振光束来产生超长且高均匀性的光学针。通过在光轴上产生、移动和合并多焦点光斑，获得具有强纵向偏振场的光针。引入遗传算法以提高优化效率并为同时求解多焦点位置提供通用方法。沿光轴的轴向半高全宽 (FWHM) 已扩展至 20.3 λ。更吸引人的是，针的 18 λ 长中心部分表现出 96.7% 的均匀性。轴向和径向的最大旁瓣分别为2%和23%。我们进一步探索了在不同焦斑融合量下针头所能达到的最大均匀长度，为设计定制长度的均匀光学针头提供参考。所提出的方法为超长且高度均匀的光学针提供了简单有效的设计过程，可在粒子加速和光学俘获方面得到广泛应用。