Generation of anomalous vector Bessel beams with varying polarization order along the propagation direction

Abstract

Vector Bessel beams (VBBs) contain non-uniform polarization distributions on the cross-section and non-diffraction characteristics, have been widely used in many fields, including optical trapping, optical microscope, optical communication, etc. Here, we propose a theoretical model to obtain anomalous-VBBs with polarization order dependent on propagation distance. Based on geometrical optics principle, the designed spiral slit allows the introduction of a continuous phase delay, which is used to generate two Bessel vortex beams with opposite chirality and topological charges. Then, by coherently superimposing these two Bessel vortex beams, an anomalous-VBB is generated and shows the polarization order dependent on the propagation distance. Arbitrary polarization orders including integers and fractions can be generated by manipulating the propagation distance. The simulation results show that the local polarization distribution measured at different distances is in good agreement with the polarization distribution of theoretical VBBs, and the local polarization order of anomalous-VBBs is inversely proportional to the propagation distance. The characteristic of this anomalous beam may intrigue the applications of VBBs in light-matter interaction, microscopy and quantum information.