title: Tight focusing of quasi-cylindrically polarized beams.
abstract: Based on vectorial diffraction theory, tight focusing properties of quasi-cylindrical polarized beams (QCPBs) composed of equal fan-shaped sectors with linear polarization are investigated. We find that, for quasi-radially polarized illumination, a weak azimuthal component emerges and the circular symmetry of focus is traded in when the total number of sector N is small, but when N≥8 it is approaching that of a perfect radially polarized beam with a deviation smaller than 5.3% and a ratio of maximum total intensity larger than 95.5%. Meanwhile, for quasi-azimuthal polarized illumination, although weak radial and longitudinal components emerge, it is also close to that of the perfect azimuthally polarized beam when N≥8 with deviation smaller than 5.3% and a ratio larger than 95.0%. These results not only reveal a deep understanding of the focusing properties of QCPBs, but also provide an important contribution toward optimization of the monolithic methods for generating vector beams.
authors.forename: Zhongsheng
authors.initials: Z
authors.lastname: Man
authors.forename: Changjun
authors.initials: C
authors.lastname: Min
authors.forename: Siwei
authors.initials: S
authors.lastname: Zhu
authors.forename: X-C
authors.initials: XC
authors.lastname: Yuan