Extending Focal Depth of Flower-Shaped Optical Vortex with Composited Spiral Zone Plate Grating

By combining a spiral zone plate (SZP) and grating, we propose single optical element, termed composited grating (CSZPG), to generate flower mode vortices with the equicohesive petals has long focal depths. Theoretical analysis reveals that CSZPG can approximately petals, it longer depths compared conventional SZP. Moreover, performance of on period, length radius is investigated. The experimental results are also presented, agreeing well theoretical predictions. unique characteristics proposed make attractive for many applications such as particle trapping imaging.