title: Minimized spot of annular radially polarized focusing beam.
abstract: We have experimentally demonstrated the measurement of a tighter focal spot generated by a radially polarized narrow-width annular beam with the double-knife-edge method. The reconstructed spot profiles indicate that sharper focus cannot be achieved by shrinking the annular aperture further. The smallest focal spot (0.0711λ(2)) is obtained in experiment with an annular factor of 0.91. An apodization function has been introduced with the consideration of the diffraction effect, which achieves good agreement with the experimental data. Our result shows that the diffraction effect should be considered with small topography structures of the incident beam.
authors.affiliation: State Key laboratory of Optoelectronic Materials and Technologies, Sun Yat-sen University, Guangzhou 510275, China.
authors.forename: Liangxin
authors.initials: L
authors.lastname: Yang
authors.forename: Xiangsheng
authors.initials: X
authors.lastname: Xie
authors.forename: Sicong
authors.initials: S
authors.lastname: Wang
authors.forename: Jianying
authors.initials: J
authors.lastname: Zhou