Three dimensional polarization control in 4Pi microscopy

An approach to obtain a diffraction-limited spherical focal spot with controllable three dimensional state of polarization in 4Pi microscopy is proposed. By combining the angular radiation pattern of a dipole antenna and vectorial diffraction method, input field at the pupil plane for creating a spherical focal spot with arbitrary three dimensionally oriented linear polarization is found analytically by solving the inverse problem. A diffraction-limited spherical spot with arbitrary three dimensional elliptical polarization can be realized by introducing a second dipole antenna oriented in the orthogonal plane with appropriate amplitude and phase differences.