The ability of light to carry and deliver orbital angular momentum (OAM) in the form of optical vortices has attracted much interest. The physical properties of light with a helical wavefront can be confined onto two-dimensional surfaces with subwavelength dimensions in the form of plasmonic vortices, opening avenues for thus far unknown light-matter interactions. Because of their extreme rotational velocity, the ultrafast dynamics of such vortices remained unexplored. Here we show the detailed spatiotemporal evolution of nanovortices using time-resolved two-photon photoemission electron microscopy. We observe both long- and short-range plasmonic vortices confined to deep subwavelength dimensions on the scale of 100 nanometers with nanometer spatial resolution and subfemtosecond time-step resolution. Finally, by measuring the angular velocity of the vortex, we directly extract the OAM magnitude of light.

Broad-area, vertical-cavity surface-emitting lasers were shown to switch their emission mode from the regular single or multilobed light fields to exhibit complex arrays of "dark beams." Examination of these dark spot arrays revealed that they consist of multiple, closely packed optical vortices: optical fields that have phase singularities and show increased complexity as the injection current level is raised. Contrary to their complex appearance, most of these light distributions are not the result of a multimode (multiple-frequency) operation but exhibit single-frequency characteristics. The dark beam patterns can be described as emanating from a spontaneous process of transverse mode locking of nearly degenerate modes, assisted by the laser nonlinearity. Surprisingly, these patterns show high resemblance to patterns generated in other nonlinear scenarios that are completely different both in scale and in mechanism.

Formation of a novel hybrid-vector spatial plasmon-soliton in a Kerr slab embedded in-between metal plates is predicted and analyzed with a modified NLSE, encompassing hybrid vector field characteristics. Assisted by the transverse plasmonic effect, the self trapping dimension of the plasmon-soliton was substantially compressed (compared to the dielectrically cladded slab case) when reducing the slab width. The practical limitation of the Plasmon-soliton size reduction is determined by available nonlinear materials and metal loss. For the extreme reported values of nonlinear index change, we predict soliton with a cross section of 300nm×30nm (average dimension of 100nm).

We demonstrate nanofocusing down to 60 nm with 800-nm light in atomically flat single-crystalline 22-nm-thick gold flakes.

We report the first experimental observations of two-photon emission from semiconductors, to the best of our knowledge, and develop a corresponding theory for the room-temperature process. Spontaneous two-photon emission is demonstrated in optically-pumped bulk GaAs and in electrically-driven GaInP/AlGaInP quantum wells.Singly-stimulated two-photon emission measurements demonstrate the theoretically predicted two-photon optical gain in semiconductors -a necessary ingredient for any realizations of future two-photon semiconductor lasers. Photon-coincidence experiment validates the simultaneity of the electrically-driven GaInP/AlGaInP two-photon emission, limited only by detector's temporal resolution.