Generation of needle beams through focusing of azimuthally polarized vortex beams by polarization-insensitive metasurfaces

Needle beams are widely used in advanced applications due to their high intensity, high resolution, and extended depth of focus. In this work, the generation of needle beams through transmitting azimuthally polarized beams to polarization-insensitive metasurfaces is presented. Defocus phase profiles and annular apertures were adopted to obtain needle beams, respectively. A relatively long depth of focus ( 16.9 λ ) with subdiffraction beam size ( 0.41 λ ) was obtained. The introduction of metasurfaces can significantly simplify an optical system compared with traditional methods utilizing complex optical elements. This study may contribute to photolithography, microscopy, particle manipulation, and acceleration.