Changeable focused field distribution of double-ring-shaped cylindrical vector beams

Based on vector diffraction theory, the focusing features of double-ring-shaped cylindrical vector (DCV) beams are studied in this paper. The intensity pattern in the vicinity of the focus can be tailored by appropriately adjusting the parameters of the ratio of the inner-to-outer ring radius and the polarization state of the incident DCV beams. It is shown that focused field with flattop or optical cage profile is easily obtained. Moreover, we also propose a new approach to generate a flattop focus with extended depth of focus and lower side-lobe levels by adding a diffractive optical element (DOE) which is cleverly loaded on the spatial light modulator (SLM). The results from this study would especially facilitate light manipulation of two types of particles with different refractive indices in only one optical-trap system.