Achieving ultra-long optical needles with a duplex vector optical field and parabolic hybrid mask

Abstract

The optical needle generated by a tightly focused vector optical field (VOF) has attracted wide attention and been applied in various areas. In previous research, two typical kinds of VOFs were generally used to generate optical needles, including radially polarized VOF (RP-VOF) and vortex azimuthally polarized VOF (VAP-VOF). Here, we propose a new kind of duplex VOF that is designed by arranging the RP-VOF and VAP-VOF in concentric belts. With the help of a binary phase mask, the optical needle of the tightly focused duplex VOF is much longer than that generated by the two conventional VOFs. The optical needle has a three-section polarization distribution, as the longitudinal component is dominant in the center, while the transverse components are at two ends along the longitudinal axis, which is different from a purely transversely polarized optical needle and optical needle with a dominant longitudinal component. Furthermore, a parabolic hybrid mask (PHM) is proposed, which can improve the length of the optical needle for the duplex VOF, RP-VOF, and VAP-VOF. When applying the duplex VOF and PHM simultaneously, an ultra-long optical needle can be achieved. The duplex VOF and PHM we propose are superior relative to other VOFs and masks in terms of generating ultra-long optical needles, which can be used in areas including optical detection, high-density storage, super-resolution imaging, and nano lithography.