Tunable focal shift induced by polarization and phase shaping

We propose a simple method to control the move and elongation of focus along the optical axis in a high-numerical aperture focusing system. By introducing the optical degree of freedom of polarization in the radial direction, a tunable focal shift and elongation of focus are achieved simply by tailoring the polarization index and the topological charge of vortex phase, without the need of additional modulations of amplitude or diffractive optical elements. These findings may be of help in the applications like optical micro-manipulation, laser processing, and imaging.