title: Long-distance axial trapping with focused annular laser beams.
abstract: Focusing an annular laser beam can improve the axial trapping efficiency due to the reduction of the scattering force, which enables the use of a lower numerical aperture (NA) objective lens with a long working distance to trap particles in deeper aqueous medium. In this paper, we present an axicon-to-axicon scheme for producing parallel annular beams with the advantages of higher efficiency compared with the obstructed beam approach. The validity of the scheme is verified by the observation of a stable trapping of silica microspheres with relatively low NA microscope objective lenses (NA = 0.6 and 0.45), and the axial trapping depth of 5 mm is demonstrated in experiment.
authors.affiliation: State Key Laboratory of Transient Optics and Photonics, Xi'an Institute of Optics and Precision Mechanics, Chinese Academy of Sciences, Xi'an, China.
authors.forename: Ming
authors.initials: M
authors.lastname: Lei
authors.forename: Ze
authors.initials: Z
authors.lastname: Li
authors.forename: Shaohui
authors.initials: S
authors.lastname: Yan
authors.forename: Baoli
authors.initials: B
authors.lastname: Yao
authors.forename: Dan
authors.initials: D
authors.lastname: Dan
authors.forename: Yujiao
authors.initials: Y
authors.lastname: Qi
authors.forename: Jia
authors.initials: J
authors.lastname: Qian
authors.forename: Yanlong
authors.initials: Y
authors.lastname: Yang
authors.forename: Peng
authors.initials: P
authors.lastname: Gao
authors.forename: Tong
authors.initials: T
authors.lastname: Ye
mesh_terms: D007834:Lasers; D007909:Lenses; D008863:Microspheres; D008962:Models, Theoretical; D052898:Optical Tweezers; D012822:Silicon Dioxide
chemical_list: D012822:Silicon Dioxide