Sub-wavelength longitudinally polarized optical needle arrays generated with tightly focused radially polarized Gaussian beam

Abstract In this paper, we proposed an effective method to generate tunable sub-wavelength longitudinal polarized optical needle arrays. Based on the vector diffraction theory, a radially polarized light beam is tailored with a self-designed binary-phase filter (BPF), which is engineered on demand by particle swarm optimization (PSO) algorithm. We are able to garner single longitudinally polarized sub-wavelength (0.433 λ ) and long (6 λ ) optical needle with almost perfect uniformity of 98%, ultrahigh beam quality of 96%, and negligible sidelobe of 15%. Furthermore, we engineer a novel multi-focus phase filter (MFPF) in combination with the initial binary filter. It is found that longitudinally polarized sub-wavelength optical needle arrays (ONAs) can be created in the focal volume. More impressively, in addition to maintaining all of properties of single light needle, the number, position, and texture of the optical needles could be mediated flexibly through the MFPF, thus leading to tunable optical needle array. The findings demonstrated here may evoke wide-ranging applications in material processing, lithography and fluorescence imaging.