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PUBLISHED, The manipulation of a Gaussian laser beam using conical diffraction in a high optical quality biaxial crystal of KGd(WO4)2 has been examined in detail with emphasis on the experimental techniques involved and intuitive explanations of the notable features. Two different optical arrangements were used to form the Pogendorff double-ring light pattern in the focal image plane. The formation of both diverging and non-diverging zeroth and first order Bessel beams was investigated. The various intensity distributions and polarization properties were measured and compared with the predictions of well-established theory., This work was supported by Science Foundation Ireland under the Research Frontiers Programme.

Internal conical diffraction produces a superposition of orthogonally polarised zero- and first-order Bessel like beams from an incident circularly polarised Gaussian beam. For right-circularly polarised light, the first-order beam has an optical vortex of charge −1. Upon propagation of the first-order beam through a second biaxial crystal, a process which is termed cascade conical refraction, the generated beam is a superposition of orthogonally polarised fields of charge 0 and −1 or 0 and −2. This spin to orbital angular momentum conversion provides a new method for the generation and annihilation of optical vortices in an all-optical arrangement that is solely dependent on the incident polarisation and vortex handedness., We acknowledge the support of Science Foundation Ireland under research grants 06/RFP/PHY029, SFI/SIRG/I1592 and 08/IN.1/I1862 and Sir Michael Berry for helpful discussions.

Conical diffraction of linearly polarised light in a biaxial crystal produces a beam with a crescent-shaped intensity profile. Rotation of the plane of polarisation produces the unique effect of spatially moving the crescent-shaped beam around a ring. We use this effect to trap microspheres and white blood cells and to position them at any angular position on the ring. Continuous motion around the circle is also demonstrated. This crescent beam does not require an interferometeric arrangement to form it, nor does it carry optical angular momentum. The ability to spatially locate a beam and an associated trapped object simply by varying the polarisation of light suggests that this optical process should find application in the manipulation and actuation of micro- and nano-scale physical and biological objects.

When a left-circularly polarised Gaussian light beam, which has spin angular momentum (SAM) J(sp) = sigmah = 1h per photon, is incident along one of the optic axes of a slab of biaxial crystal it undergoes internal conical diffraction and propagates as a hollow cone of light in the crystal. The emergent beam is a superposition of equal amplitude zero and first order Bessel like beams. The zero order beam is left-circularly polarised with zero orbital angular momentum (OAM) J(orb) = [see text]h = 0, while the first order beam is right-circularly polarized but carries OAM of J(orb) = 1h per photon. Thus, taken together the two beams have zero SAM and J(orb) = (1/2)h per photon. In this paper we examine internal conical diffraction of an elliptically polarised beam, which has fractional SAM, and demonstrate an all-optical process for the generation light beams with fractional OAM up to +/- 1h.

Symmetric directional emission of light from multisphere photonic molecules is experimentally shown in this work. The photonic molecules are illuminated in the vertical direction with a defocused laser beam. The emission is attributed to photonic nanojets generated in the structure. Furthermore, spectral analysis exhibit whispering gallery mode resonances of coupled and uncoupled modes. A benzene molecule-like structure consisting of a 7-microspheres cyclic photonic molecule shows a field emission pattern similar to the spatial distribution of the orbitals of the benzene molecule.

In this work, we present a novel method to reveal azimuthal whispering gallery modes (WGMs) in a spherical microcavity coated with a nano-meter thick polyelectrolyte shell and one monolayer of CdTe semiconductor quantum dots. The new approach in this experiment is based on the deformation of the spherical shape in a non-contact way using the radiation pressure from a laser beam, which causes the lifting of the degeneracy of the WGMs. The resonance peak linewidth and splitting parameters can be efficiently controlled by the strength of the radiation pressure and the elastic properties of the surface shell.