Generation of optical vortex dipole from superposition of two transversely scaled Gaussian beams

Abstract

We propose a distinct concept on the generation of optical vortex through coupling between the amplitude and phase differences of the superposing beams. For the proof-of-concept demonstration, we propose a simple free-space optics recipe for the controlled synthesis of an optical beam with a vortex dipole by superposing two transversely scaled Gaussian beams. The experimental demonstration using a Sagnac interferometer introduces the desired amount of radial shear and linear phase difference between the two out-of-phase Gaussian beams to create a vortex pair of opposite topological charge in the superposed beam. Flexibility to tune their location and separation using the choice of direction of the linear phase difference and the amount of amplitude difference between the superposing beams has potential applications in optical tweezers and traps utilizing the local variation in angular momentum across the beam cross section.

Generation of singular optical beams from fundamental Gaussian beam using Sagnac interferometer

“…Propagation of optical beams with embedded vortices exhibit unique and fascinating dynamics [32,33]. Moreover, understanding the propagation dynamics of the optical vortex field is necessary to treat them as optical beams [26]. Due to the symmetry in introducing the amplitude and phase differences between the two superposing Gaussian beams, in general it can be inferred that the generated vortex beam could propagate for a long distance maintaining its characteristics.…”

“…It is well known that the vortices are created and annihilated as dipoles. A vortex dipole is shown to be born out of such a stationary point by introducing a radial shear and a linear phase difference between the superposing Gaussian beams using an inherently stable Sagnac interferometer [26][27][28][29]. The theoretical approach also hinted at a coupling that exists between the amplitude and phase differences introduced between the individual superposing beams.…”