Conical refraction of a high-M2 laser beam

Abstract

We report on experiments with conical refraction of laser beams possessing a high beam propagation parameter M2. With beam propagation parameter values M2=3 and M2=5, unusual Lloyd's distributions with correspondingly three and five dark rings were observed. In order to explain this phenomenon, we extend the dual-cone model of the conical refraction that describes it as a product of interference of two cones that converge and diverge behind the exit facet of the crystal. In the extended model, these converging/diverging cones are represented as the cone-shaped quasi-Gaussian beams possessing the M2 parameter of an original beam. In this formalism, a beam-waist of these cone-shaped beams is proportional to the M2 value and defines the area of their interference which is a width of the Lloyd's ring. Therefore, the number of dark rings in the Lloyd distribution is defined by the M2 value and can be much greater than unity. The results of the numerical simulations within the extended dual-cone model are in excellent agreement with the experiment.