Experimental study of internal conical refraction in a biaxial crystal with Laguerre–Gauss light beams

Abstract

The effect of internal conical refraction (CR) in a biaxial crystal was studied using Laguerre–Gauss light beams with and 2, while the lowest-order beam was used as a reference. The transition from ordinary double refraction to CR was examined. It has been shown that double refraction of an beam forms two focal spots containing dark stripes. These stripes evolve into dark rings over an annular focal image when CR is established, and it results in a fine-structure of bright focal rings with different intensities. In a sharp contrast to the lowest-order reference, the multiring focal structure has a distinct asymmetry with respect to the focal image plane. It has been shown that bright off-axis ‘hot spot’ can be formed on the far-field profiles of outgoing light beams when the biaxial crystal is slightly tilted, and a small angle between the propagation axis of the beam and the optic axis of the crystal arises. These off-axis light structures emerge as either a charge-one optical vortex or a zero-charge spot with annihilated vorticity. Polarization selection reveals or Bessel-like profiles of the corresponding ‘hot spots’, and a complex pattern of forked fringes in the dark region near the beam core.