Conical refraction mode of an optical resonator.

The fundamental mode of a conical refraction resonator, i.e., an optical cavity where light experiences conical refraction (CR) from a biaxial crystal, is experimentally demonstrated in the plano-concave cavity configuration. We have discovered that the fundamental CR mode is characterized by the polarization and intensity structures of CR beams between the plane mirror and CR crystal, and it resembles the fundamental Gaussian mode with homogeneous polarization between the crystal and concave mirror. We theoretically explained this fundamental CR mode using the dual cone model and symmetry of the CR phenomenon and confirmed this explanation by numerical simulations.

Blue-detuned optical ring trap for Bose-Einstein condensates based on conical refraction.

We present a novel approach for the optical manipulation of neutral atoms in annular light structures produced by the phenomenon of conical refraction occurring in biaxial optical crystals. For a beam focused to a plane behind the crystal, the focal plane exhibits two concentric bright rings enclosing a ring of null intensity called the Poggendorff ring. We demonstrate both theoretically and experimentally that the Poggendorff dark ring of conical refraction is confined in three dimensions by regions of higher intensity. We derive the positions of the confining intensity maxima and minima and discuss the application of the Poggendorff ring for trapping ultra-cold atoms using the repulsive dipole force of blue-detuned light. We give analytical expressions for the trapping frequencies and potential depths along both the radial and the axial directions. Finally, we present realistic numerical simulations of the dynamics of a 87Rb Bose-Einstein condensate trapped inside the Poggendorff ring which are in good agreement with corresponding experimental results.

Polarization tailored novel vector beams based on conical refraction.

Coherent vector beams with involved states of polarization (SOP) are widespread in the literature, having applications in laser processing, super-resolution imaging and particle trapping. We report novel vector beams obtained by transforming a Gaussian beam passing through a biaxial crystal, by means of the conical refraction phenomenon. We analyze both experimentally and theoretically the SOP of the different vector beams generated and demonstrate that the SOP of the input beam can be used to control both the shape and the SOP of the transformed beam. We also identify polarization singularities of such beams for the first time and demonstrate their control by the SOP of the input beam.

Super-Gaussian conical refraction beam.

We demonstrate the transformation of Gaussian input beams into super-Gaussian beams with a quasi flat-top transverse profile by means of the conical refraction phenomenon by adjusting the ratio between the ring radius and the waist radius of the input beam to 0.445. We discuss the beam propagation of the super-Gaussian beam and show that it has a confocal parameter three times larger than the one that would be obtained from a Gaussian beam. The experiments performed with a KGd(WO4)2 biaxial crystal are in good agreement with the theoretical predictions.

Generating a three-dimensional dark focus from a single conically refracted light beam.

We report here the generation of a three-dimensional (3D) dark focus from a single focused monochromatic Gaussian beam that undergoes conical refraction when it propagates along one of the optic axes of a biaxial crystal. We study the resulting ring intensity pattern behind the crystal as a function of the ratio between the ring radius and the beam waist and derive the particular parameter values for which a 3D dark focus with null intensity at the ring center is formed. We have performed experiments with a KGd(WO(4))(2) biaxial crystal, reporting the generation of a bottle beam in full agreement with our theoretical investigations.

Optical vault: a reconfigurable bottle beam based on conical refraction of light.

We employ conical refraction of light in a biaxial crystal to create an optical bottle for photophoretic trapping and manipulation of particles in gaseous media. We show that by only varying the polarization state of the input light beam the optical bottle can be opened and closed in order to load and unload particles in a highly controllable manner.

Wave-vector and polarization dependence of conical refraction.

We experimentally address the wave-vector and polarization dependence of the internal conical refraction phenomenon by demonstrating that an input light beam of elliptical transverse profile refracts into two beams after passing along one of the optic axes of a biaxial crystal, i.e. it exhibits double refraction instead of refracting conically. Such double refraction is investigated by the independent rotation of a linear polarizer and a cylindrical lens. Expressions to describe the position and the intensity pattern of the refracted beams are presented and applied to predict the intensity pattern for an axicon beam propagating along the optic axis of a biaxial crystal.