title: Creating a spherical focal spot with spatially modulated radial polarization in 4Pi microscopy.
abstract: We propose an approach to obtain a diffraction-limited spherical focal spot in 4Pi microscopy. By combining the dipole antenna radiation pattern and the Richards-Wolf vectorial diffraction method, an input field at a pupil plane of aplanatic objective lenses for generating a spherical spot can be found analytically by solving the inverse problem. The required field at the pupil plane is found to be a radial polarization with spatial amplitude modulation. With spatial phase modulation, two identical spherical spots with diffraction-limited size and variable distance along the optical axis can also be obtained.
authors.affiliation: Electro-Optics Graduate Program, University of Dayton, 300 College Park, Dayton, Ohio, 45469-0245, USA.
authors.forename: Weibin
authors.initials: W
authors.lastname: Chen
authors.forename: Qiwen
authors.initials: Q
authors.lastname: Zhan