Axial multifocal binary-phase zone plate for high numerical aperture focusing

This is the authors' abstract. We don't add key points for this paper.

Binary-phase zone plates (BPZPs) are proposed for generating two foci along the optical axis of a high numerical aperture objective. The radii of BPZPs are given by an analytical expression, in which the axial shifting distance of two foci is included. By changing the axial shifting distance, a set of BPZPs can be designed for achieving tunable two foci in the optical axial direction of the objective. Theoretical analysis and simulation results prove that the tunable axial two foci can be realized successfully, and furthermore, the intensity distribution of focal spots with special shapes (optical needle and optical bubble) can also be created by using BPZPs with suitable axial shifting distance. In addition, axial multifocal spots array can also be realized by superposition of multiple BPZPs with different axial shifting distances.