Bending of electromagnetic waves in all-dielectric particle array waveguides

We propose and demonstrate experimentally an alternative approach for realizing subwavelength photonic structures, exploiting the waveguiding properties of chains of high-index dielectric disks with both electric and magnetic dipole resonances. We reveal that the electromagnetic energy can be efficiently guided through sharp corners by means of the mode polarization conversion at waveguide bends. We confirm experimentally the guidance through a 90° bend in the microwave frequency range.This work was supported by the Ministry of Education and Science of the Russian Federation (Project 11.G34.31.0020, GOSZADANIE 2014/190, Zadanie No. 3.561.2014/K, 14.584.21.0009 10), by Russian Foundation for Basic Research, the Dynasty Foundation (Russia), the Australian Research Council via Future Fellowship Program (No. FT110100037), and the Australian National University

Campsites of the Southern Urals Nomads in the Middle of the I Millennium BC (according to data from the Bannoye – Sabakty – Karabalykty Lake System)

The paper deals with the materials from three sites, namely the settlement Bannoye-5a (Berezki), Telyashevo-4 and Sabakty-3/5. They are discovered with ceramics of the early nomads (late V – late IV century BC). All these sites are situated within a narrow strip of mountain steppes along the eastern slope of the Southern Urals (modern Abzelilovsky district of the Republic of Bashkortostan). It is on the same latitude as Magnitogorsk. The settlement Bannoye-5a (Berezki) was studied in 1972–1976 and 2004–2005. The received materials were analyzed and showed three points of spread early nomadic ceramics. Two of them were revealed by excavations and are rather small in size. Also a similar situation was at Telyashevo-4 settlement. It is shown that all three sites can be interpreted as nomadic campsites. When the author analyzes all the information about the spread area of Southern Ural nomads in the middle of the I millennium BC, the author can conclude that the campsites and other types of settlements close to them were quite common (more than 30 sites are currently recorded). It is particularly complicated to find and register such kind of sites, however, studying them is the only way to learn something new about their household, spread and land development

Phase Transitions in Isolated Vortex Chains

In very anisotropic layered superconductors (e.g. Bi$_2$Sr$_2$CaCu$_2$O$_x$) a tilted magnetic field can penetrate as two co-existing lattices of vortices parallel and perpendicular to the layers. At low out-of-plane fields the perpendicular vortices form a set of isolated vortex chains, which have recently been observed in detail with scanning Hall-probe measurements. We present calculations that show a very delicate stability of this isolated-chain state. As the vortex density increases along the chain there is a first-order transition to a buckled chain, and then the chain will expel vortices in a continuous transition to a composite-chain state. At low densities there is an instability towards clustering, due to a long-range attraction between the vortices on the chain, and at very low densities it becomes energetically favorable to form a tilted chain, which may explain the sudden disappearance of vortices along the chains seen in recent experiments.Comment: 9 pages, 10 figure

Coherent control of topological states in an integrated waveguide lattice

Topological photonics holds the promise for enhanced robustness of light localization and propagation enabled by the global symmetries of the system. While traditional designs of topological structures rely on lattice symmetries, there is an alternative strategy based on accidentally degenerate modes of the individual meta-atoms. Using this concept, we experimentally realize topological edge state in an integrated optical nanostructure based on the array of silicon nano-waveguides, each hosting a pair of degenerate modes at telecom wavelengths. Exploiting the hybrid nature of the topological mode formed by the superposition of waveguide modes with different symmetry, we implement coherent control of the topological edge state by adjusting the phase between the degenerate modes and demonstrating selective excitation of bulk or edge states. The resulting field distribution is imaged via third harmonic generation allowing us to quantify the localization of topological modes as a function of the relative phase of the excitations. Our results highlight the impact of engineered accidental degeneracies on the formation of topological phases, extending the opportunities stemming from topological nanophotonic systems.Comment: 17 pages, 4 figure

Laser-driven pointed acceleration of electrons with preformed plasma lens

The simultaneous laser-driven acceleration and angular manipulation of the fast electron beam is experimentally demonstrated. The bunch of multi-MeV energy charged particles is generated during the propagation of the femtosecond laser pulse through the near-critical plasma slab accompanied by plasma channeling. Plasma is formed by the controlled breakdown of a thin-tape target by a powerful nanosecond prepulse. The electron beam pointing approach is based on the refraction of a laser pulse in the presence of a strong radial density gradient in the breakdown of the tape with a small displacement of the femtosecond laser beam relative to the breakdown symmetry axis. A shift of several micrometers makes it possible to achieve beam deflection by an angle up to 10 degrees with acceptable beam charge and spectrum conservation. This opens up opportunities for in-situ applications for scanning objects with an electron beam and the multistage electron beam energy gain in consecutive laser accelerators without bulk magnetic optics for particles. Experimental findings are supported by numerical Particle-In-Cell calculations of laser-plasma acceleration and hydrodynamic simulations.Comment: Submitted to PPC