We demonstrate three-dimensional trapping of low-index particles (20-μm-diameter hollow glass spheres in water) by using a single, strongly focused, stationary dark optical vortex laser beam. The holographically generated vortex, which is similar to a ${\text{TEM}}_{01}^{*}$ mode beam, was also used to trap and form ring patterns of high-index particles.

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Optical vortex-soliton filaments are observed in a bulk self-defocusing Kerr nonlinear refractive medium. The dark cylindrical core, located at the axis of a 2π helical phase ramp, is stationary and stable, with a size that depends inversely on the field strength. Wave guiding of a weak probe beam within the core is reported. A single optical vortex soliton was experimentally created using a quasihelical phase mask. Pairs having opposite topological charge were experimentally and numerically investigated using a convective Kelvin-Helmholtz instability of dark soliton stripes.

Experimental and numerical techniques allowed us to predict and verify the existence of a robust phase singularity in the spatial coherence function when a vortex is present. Though observed in the optical domain, this phenomenon may occur in any partially coherent vortex wave.

Spatial dark-soliton (SDS) stripes are experimentally found in the transverse plane of a laser beam that passes through a rectilinear diffraction screen before propagating in a self-defocusing nonlinear material. Materials with different mechanisms of nonlinearity manifest the same qualitative results. The SDS nature of the observed phenomenon is verified by numerical simulations of the (2+1)-D nonlinear Schrödinger equation, analytical solutions for the (1+1)-D case, and their comparison with experimental data.

I propose to use as a window the dark core of an optical vortex to examine a weak background signal hidden in the glare of a bright coherent source. Applications such as the detection of an astronomical object, forward-scattered radiation, and incoherent light are described whereby signal enhancements of at least 7 orders of magnitude may be achieved.