title: Versatile generation of optical vortices based on paraxial mode expansion.
abstract: We demonstrate a simple and versatile method for generating various configurations of optical vortices from a Gaussian light beam by using glass plates and an astigmatic mode converter (AMC). The glass plates are inserted into the Gaussian beam to imprint nodal lines along the edges, and the AMC then transforms the beam with the nodes into a vortex beam. The procedures are discussed in terms of a transverse-mode expansion of the paraxial light beam, in which each Hermite-Gaussian mode is converted into the corresponding Laguerre-Gaussian mode by the AMC. We generated several vortex configurations, and the results show good agreement with the theoretical predictions.