title: Circular Dammann grating under high numerical aperture focusing.
abstract: Circular Dammann grating (CDG) under high numerical aperture (NA) focusing is described based on Richards-Wolf vectorial diffraction theory in this paper. Several CDGs are presented under the condition of NA=0.9 with the illumination of circularly polarized plane-wave laser beams. Numerical results show that the sizes of these circular patterns with equal-intensity are in the wavelength scale, and doughnut-shaped central spots and dark rings are in the subwavelength width. To verify this kind of CDG, a binary pure-phase three-order CDG is fabricated to produce a dark center pattern surrounded by three concentric bright rings. The corresponding intensity distribution of the pattern on the focal plane of a high-NA objective (NA=0.9) is measured, and the results agree well with theoretical simulations. This kind of CDG with annular patterns of equal-intensity in the wavelength scale should be highly interesting for its potential applications in optical trapping, stimulated emission depletion (STED) microscopy, and the study of singular optics, as well as annular array illumination.
authors.affiliation: Lab of Information Optics and Optoelectronics Techniques, Shanghai Institute of Optics and Fine Mechanics, Academia Sinica, P.O. Box 800-211, Shanghai 201800, China.
authors.forename: Junjie
authors.initials: J
authors.lastname: Yu
authors.forename: Changhe
authors.initials: C
authors.lastname: Zhou
authors.forename: Wei
authors.initials: W
authors.lastname: Jia
authors.forename: Anduo
authors.initials: A
authors.lastname: Hu
authors.forename: Shaoqing
authors.initials: S
authors.lastname: Wang
authors.forename: Jianyong
authors.initials: J
authors.lastname: Ma