A simple roadmap is established for the construction of the smallest three-dimensional (3D) isotropic focal spots. It is achieved in a 4Pi configuration by imposing a restriction/condition of equal transverse and longitudinal spot sizes to determine the position of an annular aperture and then optimize its size. The calculations were performed for cylindrically symmetric radial, azimuthal, and circular polarizations for the cases of in-phase and out-of-phase counter-propagating beams as well as when a vortex was added to the beams. A diffraction-limited bright 3D isotropic spot containing solely longitudinal or transverse electric field components is obtained, while the 3D dark spot can be formed from one of two complementary combinations, each containing both transverse and longitudinal field components.
© 2013 Optical Society of America
Original Manuscript: July 31, 2013
Manuscript Accepted: August 22, 2013
Published: September 18, 2013
Svetlana N. Khonina and Ilya Golub, "Engineering the smallest 3D symmetrical bright and dark focal spots," J. Opt. Soc. Am. A 30, 2029-2033 (2013)