Phase distributions accompanying the conical diffraction through a Pasteur acentric biaxial crystal, displayed with Bi2ZnOB2O6

The conical diffraction of an optical wave through a biaxial crystal leads to an electric vector field with a specific polarization and phases distributions assessable from a unitary operator. The optical activity, if the crystal is a Pasteur acentric one, modifies deeply the phenomenon and two phases are required instead of one for pure birefringence. These modifications in a Bi2ZnOB2O6 crystal were characterized using a polarimetric method and an interferential conoscope equipped with a liquid crystal retarder allowing the measurement of the Pancharatman phase difference between the electric field under study and a vertically or horizontally polarized reference beam. The orbital angular momentum is linked with this phase. All the experimental data and their theoretical description are in reasonably good agreement without adjusting any optical parameters. •An acentric Pasteur biaxial Bi2ZnOB2O6 single crystal oriented perpendicular to the optical axis is described as a bi-anisotropic medium.•The conical diffraction involves two parameters for the polarization: the Euler angles on the Poincaré sphere determined by a polarimetric method.•The conical diffraction involves two phase parameters (instead of one for pure birefringence) determined by an interferential conoscope.•The link between the OAM and the Pancharatman phase difference between the electric field under study and a vertically or horizontally polarized reference is provided.•All the experimental data and their theoretical description are in reasonably good agreement without adjusting any optical parameters, while it is necessary to include the axial dependence of the refractive indices.