The generation of ultra-long longitudinally polarized optical needle with multi-belt complex phase filter

In the paper, a multi-belt complex phase filter was optimized by increasing the number of belts and changing phase and amplitude parameters of the filter. By focusing radially polarized sinh-Gaussian beams in single objective system with high-NA lens, longitudinal polarized optical needles were obtained with super-resolution in focal plane. And the super-resolution optical needle owned 36.6 lambda depth of focus and 0.42 lambda of full-width at half-maximum. The aspect ratio of the obtained optical needle was 87.14. The beam quality reached to 87.7%. The results demonstrated that the optimized multi-belt complex phase filter can lengthen depth of focus and compress transverse size simultaneously. The obtained longitudinally polarization optical needles can be used in the fields of optical data storage, super-resolution imaging, particle trapping, nanolithography and so on.