Avi Niv

Geometrodynamics of spinning light

The semiclassical evolution of spinning particles has recently been re-examined in condensed matter physics, high-energy physics, and optics, resulting in the prediction of the intrinsic spin Hall effect associated with the Berry phase. A fundamental origin of this effect is related to the spin–orbit interaction and topological monopoles. Here, we report a unified theory and a direct observation of two mutual phenomena: a spin-dependent deflection (the spin Hall effect) of photons and the precession of the Stokes vector along the coiled ray trajectory of classical geometrical optics. Our measurements are in perfect agreement with theoretical predictions, thereby verifying the dynamical action of the topological Berry-phase monopole in the evolution of light. These results may have promising applications in nano-optics and can be immediately extrapolated to the evolution of massless particles in a variety of physical systems. The spin Hall effect, an interaction between particles because of their intrinsic spin, is a central tenet in the field of spintronics. The direct observation of an optical equivalent of the spin Hall effect is now reported.

Polarization dependent focusing lens by use of quantized Pancharatnam–Berry phase diffractive optics

Quantized Pancharatnam–Berry phase diffractive optics using computer-generated space-variant subwavelength dielectric grating is presented. The formation of the geometrical phase is done by discrete orientation of the local subwavelength grating. We discuss a theoretical analysis and experimentally demonstrate a quantized geometrical blazed phase of polarization diffraction grating, as well as polarization dependent focusing lens for infrared radiation at wavelength 10.6 μm.

Observation of the spin-based plasmonic effect in nanoscale structures.

Observation of surface-plasmon phenomena that are dependent upon the handedness of the circularly polarized incident light (spin) is presented. The polarization-dependent near-field intensity distribution obtained in our experiment is attributed to the presence of a geometric phase arising from the interaction of light with an anisotropic and inhomogeneous nanoscale structure. A near-field vortex surface mode with a spin-dependent topological charge was obtained in a plasmonic microcavity. The remarkable phenomenon of polarization-sensitive focusing in a plasmonic structure was also demonstrated.

Formation of helical beams by use of Pancharatnam–Berry phase optical elements

Spiral phase elements with topological charges based on space-variant Pancharatnam-Berry phase optical elements are presented. Such elements can be achieved by use of continuous computer-generated space-variant subwavelength dielectric gratings. We present a theoretical analysis and experimentally demonstrate spiral geometrical phases for infrared radiation at a wavelength of 10.6microm .

Manipulation of the Pancharatnam phase in vectorial vortices.

Linearly polarized vectorial vortices are analyzed according to their Pancharatnam phase and experimentally demonstrated using a geometric phase element consisting of space-variant subwavelength gratings. It is shown that in the absence of a Pancharatnam phase, stable vectorial vortices that have no angular momentum arise. In contrast, if a Pancharatnam phase is present the vectorial vortices have orbital angular momentum and collapse upon propagation.

Polarization beam-splitters and optical switches based on space-variant computer-generated subwavelength quasi-periodic structures

Polarization beam-splitters and optical switches based on subwavelength quasi-periodic structures are presented. By locally controlling the orientation and period of the subwavelength grooves, birefringent elements for which the optical axes vary periodically, are realized. We present a theoretical discussion of these elements, as well as a detailed description of the design and realization procedures. We show experimental results for infra-red radiation at a wavelength of 10.6 μm.

Propagation-invariant vectorial Bessel beams obtained by use of quantized Pancharatnam-Berry phase optical elements

Propagation-invariant vectorial Bessel beams with linearly polarized axial symmetry based on quantized Pancharatnam-Berry phase optical elements are described. The geometric phase is formed through the use of discrete computer-generated space-variant subwavelength dielectric gratings. We have verified the polarization properties of our elements for laser radiation at 10.6-microm wavelength and also demonstrated propagation-invariant, controlled rotation of a propeller-shaped intensity pattern through the simple rotation of a polarizer.

Solar energy enhancement using down-converting particles: A rigorous approach

The efficiency of a single band-gap solar cell is specified by the Shockley-Queisser limit, which defines the maximal output power as a function of the solar cell’s band-gap. One way to overcome this limit is by using a down-conversion process whereupon a high energy photon is split into two lower energy photons, thereby increasing the current of the cell. Here, we provide a full analysis of the possible efficiency increase when placing a down-converting material on top of a pre-existing solar cell. We show that a total 7% efficiency improvement is possible for a perfectly efficient down-converting material. Our analysis covers both lossless and lossy theoretical limits, as well as a thermodynamic evaluation. Finally, we describe the advantages of nanoparticles as a possible choice for a down-converting material.

Formation of linearly polarized light with axial symmetry by use of space-variant subwavelength gratings

We present a novel method for forming linearly polarized axially symmetric beams with various polarization orders that is based on computer-generated space-variant subwavelength gratings. We introduce and experimentally demonstrate that our space-variant polarization state manipulations are accompanied by a phase modification of a helical structure that results from the Pancharatnam-Berry phase. We have verified the polarization properties of our gratings for laser radiation at 10.6-microm wavelength.

Space-variant polarization manipulation of a thermal emission by a SiO2 subwavelength grating supporting surface phonon-polaritons

Space-variant polarization manipulation of thermal emission in a narrow spectral-peak is presented. The emission is attributed to surface phonon-polariton excitation from space-variant subwavelength SiO/sub 2/ gratings. We experimentally demonstrated thermal emission in an axially symmetric polarization distribution.