Generating and shifting a spherical focal spot in a 4Pi focusing system illuminated by azimuthally polarized beams

We aim to theoretically investigate the focusing property of a 4Pi configuration under the illumination of azimuthally polarized high-order Bessel-Gaussian beams. The radial component is produced in the focal region through the introduction of a spiral phase plate. The focal region differs from the zero radial intensity component of the azimuthally polarized beams without the spiral phase plate. The spherical focal spot is generated by selecting an appropriate annular obstruction. The position of the focal spot can be shifted.