Engineering of high purity ultra-long optical needle field through reversing the electric dipole array radiation

TLDR

The study introduces a method to generate a high‑purity longitudinally polarized optical field with an exceptionally long depth of focus using a high‑NA objective lens. The method derives the necessary pupil‑plane field by reversing the radiation from a near‑focus electric dipole array, enabling the formation of an ultra‑long optical needle field. Numerical simulations show the engineered field achieves up to 8λ depth of focus while preserving a diffraction‑limited spot size (<0.43λ) and high longitudinal polarization purity, and a simplified discrete pupil filter yields marked performance gains over prior complex filters.

Abstract

We report a new method to create high purity longitudinally polarized field with extremely long depth of focus in the focal volume of a high numerical aperture (NA) objective lens. Through reversing the radiated field from an electric dipole array situated near the focus of the high-NA lens, the required incident field distribution in the pupil plane for the creation of an ultra-long optical needle field can be found. Numerical examples demonstrate that an optical needle field with a depth of focus up to 8λ is obtainable. Throughout the depth of focus, this engineered focal field maintains a diffraction limited transverse spot size (<0.43λ) with high longitudinal polarization purity. From the calculated pupil plane distribution, a simplified discrete complex pupil filter can be designed and significant improvements over the previously reported complex filters are clearly demonstrated.