Optical Tweezers With Fractional Fractal Zone Plate

Free-space propagations of the optical beams generated by the fractal zone plates with fractional structural parameters [i.e., fractional fractal zone plate (FZP)] are analytically studied in this paper. The results demonstrate that the axial location of the main focus and axial distance between two neighboring foci of the fractional FZP beam can be precisely customized. Furthermore, we first demonstrate optical manipulation with the fractional FZP beam. The experimental results verified that such an FZP beam can simultaneously trap multiple particles positioned in different focal planes of the beam, owing to the multiple foci and self-reconstruction property of the FZP beam. The customized locations of trapped particles can also be realized by the fractional FZP beam, which would be useful for constructing three-dimensional optical tweezers.