title: Focusing properties of Fresnel zone plates with spiral phase.
abstract: Focusing properties of Fresnel zone plates with spiral phase with integer and fractional topological charges illuminated by plane wave are studied. Numerical results show that hollow beams can be generated and can also be controlled by the number of the zones and the topological charge, which implies the potential applications of such kind of zone plate in trapping and manipulating particles.
authors.affiliation: Department of Physics, Zhejiang University, Hangzhou 310027, China.
authors.forename: Binzhi
authors.initials: B
authors.lastname: Zhang
authors.forename: Daomu
authors.initials: D
authors.lastname: Zhao