title: Generating doughnut-shaped beams with large charge numbers by use of liquid-crystal spiral phase plates.
abstract: Liquid-crystal spiral phase plates with cell gaps of 7 and 20 microm have been used to generate doughnut-shaped beams (doughnut beams) with charges of 1 and 4, respectively. Stacking these liquid-crystal spiral phase plates yielded doughnut beams with charge numbers up to 8. High efficiency and flexibility are the advantages of generating doughnut beams by stacking liquid-crystal spiral phase plates. Interference of doughnut beams generated by liquid-crystal spiral phase plates and plane waves has been studied. Fingerlike interference patterns were obtained with a doughnut beam tilted from a Gaussian beam; spiral fanlike patterns were obtained with a doughnut beam and a Gaussian beam collimated coaxially. The experimental results are supported qualitatively by simulation. By rotating a glass slide in the path of the Gaussian beam, one can rotate the fanlike interference pattern in a controlled fashion. With the liquid-crystal display technology that we have developed and report here, these liquid-crystal spiral phase plates should find applications in optical tweezers.
authors.affiliation: School of Electrical and Electronic Engineering, Nanyang Technological University, Nanyang Avenue, Singapore 639798.
authors.forename: Q
authors.initials: Q
authors.lastname: Wang
authors.forename: X W
authors.initials: XW
authors.lastname: Sun
authors.forename: P
authors.initials: P
authors.lastname: Shum