Switchable lasing in coupled multimode microcavities

We propose the new concept of a switchable multimode microlaser. As a generic, realistic model of a multimode microresonator a system of two coupled defects in a two-dimensional photonic crystal is considered. We demonstrate theoretically that lasing of the cavity into one selected resonator mode can be caused by injecting an appropriate optical pulse at the onset of laser action (injection seeding). Temporal mode-to-mode switching by re-seeding the cavity after a short cool-down period is demonstrated by direct numerical solution. A qualitative analytical explanation of the mode switching in terms of the laser bistability is presented.Comment: Accepted for publication in Physical Review Letters. Published, somewhat shortened versio

Radiation pattern of a classical dipole in a photonic crystal: photon focusing

The asymptotic analysis of the radiation pattern of a classical dipole in a photonic crystal possessing an incomplete photonic bandgap is presented. The far-field radiation pattern demonstrates a strong modification with respect to the dipole radiation pattern in vacuum. Radiated power is suppressed in the direction of the spatial stopband and strongly enhanced in the direction of the group velocity, which is stationary with respect to a small variation of the wave vector. An effect of radiated power enhancement is explained in terms of \emph{photon focusing}. Numerical example is given for a square-lattice two-dimensional photonic crystal. Predictions of asymptotic analysis are substantiated with finite-difference time-domain calculations, revealing a reasonable agreement.Comment: Submitted to Phys. Rev.

Hybrid photonic-bandgap accelerating cavities

In a recent investigation, we studied two-dimensional point-defected photonic bandgap cavities composed of dielectric rods arranged according to various representative periodic and aperiodic lattices, with special emphasis on possible applications to particle acceleration (along the longitudinal axis). In this paper, we present a new study aimed at highlighting the possible advantages of using hybrid structures based on the above dielectric configurations, but featuring metallic rods in the outermost regions, for the design of extremely-high quality factor, bandgap-based, accelerating resonators. In this framework, we consider diverse configurations, with different (periodic and aperiodic) lattice geometries, sizes, and dielectric/metal fractions. Moreover, we also explore possible improvements attainable via the use of superconducting plates to confine the electromagnetic field in the longitudinal direction. Results from our comparative studies, based on numerical full-wave simulations backed by experimental validations (at room and cryogenic temperatures) in the microwave region, identify the candidate parametric configurations capable of yielding the highest quality factor.Comment: 13 pages, 5 figures, 3 tables. One figure and one reference added; minor changes in the tex

Hemispheric Asymmetry Gender Differences in Preadolescent Children

Background: Investigating various postnatal parameters of cerebral hemispheres is of great practical value.Objective: To study gender differences in hemispheric parameters and interhemispheric interactions in preadolescent children.Materials and methods: The retrospective study assessed archived brain magnetic resonance images of 60 eight-year-old boys and 60 eight-year-old girls. The analyzed parameters were as follows: 1) hemispheric length; 2) hemispheric width; 3) hemispheric height; 4) width-longitudinal index of a hemisphere; 5) altitude-longitudinal index of a hemisphere; 6) length of frontal lobes; 7) length of parietal lobes; 8) length of occipital lobes; 9) length of temporal lobes. Quantitative indicators were assessed for normal distribution using the Kolmogorov–Smirnov test. Source data were accumulated and arranged in Microsoft Excel 2016 spreadsheets. Statistica 10.0 was used for the statistical analysis. The results were considered statistically significant with P < 0.05.Results: The analysis of cephalometric indicators suggests sex-related variation in the cerebral hemispheres. Based on the obtained data we can identify morphometric parameters of interhemispheric variability that may act as one of the morphometric criteria for the brain asymmetry. The study results can be widely used for neuroimaging.Conclusions: We determined cephalometric reference values for various cerebral hemispheres parts in preadolescent children

Theory of Cherenkov radiation in periodic dielectric media: Emission spectrum

The Cherenkov radiation is substantially modified in the presence of a medium with a nontrivial dispersion relation. We consider Cherenkov emission spectra of a point charge moving in general three- (3D) and two-dimensional (2D) photonic crystals. Exact analytical expressions for the spectral distribution of the radiated power are obtained in terms of the Bloch mode expansion. The resulting expression reduces to a simple contour integral (3D case) or a one-dimensional sum (2D case) over a small fraction of the reciprocal space, which is defined by the generalized Cherenkov condition. We apply our method to a specific case of an electron moving with different velocities in a 2D square-lattice photonic crystal. Our method demonstrates an excellent agreement with numerically rigorous finite-difference time-domain calculations while being less demanding on computational resources.Comment: to appear in Phys. Rev.

Plasmonic nanoparticle monomers and dimers: From nano-antennas to chiral metamaterials

We review the basic physics behind light interaction with plasmonic nanoparticles. The theoretical foundations of light scattering on one metallic particle (a plasmonic monomer) and two interacting particles (a plasmonic dimer) are systematically investigated. Expressions for effective particle susceptibility (polarizability) are derived, and applications of these results to plasmonic nanoantennas are outlined. In the long-wavelength limit, the effective macroscopic parameters of an array of plasmonic dimers are calculated. These parameters are attributable to an effective medium corresponding to a dilute arrangement of nanoparticles, i.e., a metamaterial where plasmonic monomers or dimers have the function of "meta-atoms". It is shown that planar dimers consisting of rod-like particles generally possess elliptical dichroism and function as atoms for planar chiral metamaterials. The fabricational simplicity of the proposed rod-dimer geometry can be used in the design of more cost-effective chiral metamaterials in the optical domain.Comment: submitted to Appl. Phys.

Strong mode coupling, bistable lasing, and switching mode dynamics in twin coupled microcavities

ABSTRACT Bistable lasing in twin coupled microcavities is demonstrated analytically and numerically, underlying a new principle of a multiple-wavelength microlaser where the lasing wavelength is switched by locking into the desired mode in a multimode resonator. The bistability appears due to an interplay between coherent and incoherent mode interaction processes, assisted by similarity between the spatial intensity distribution of the modes in the gain region. The wavelength switching dynamics in a model system of twin defects in a photonic crystal is explained on the basis of the theoretical analysis presented

Influence of electrolitic solution of silver on functional fctivity of rabbit neutrophils

To evaluate the activity of microbicidal system of neutrophylic granulocytes while stimulated by different doses of electrolytic solution of silver (ESS) to increase the absorbing and digesting potential of microbic bodies in phogocytosis. In the research there were used 44 male rabbits of equal weight. After obtaining check index of phagocytosis the investigated doses of ESS were given intravenously with saccharose. In 30, 60 and 120 minutes blood samples were taken to investigate the core parameters of phagocytic activity of neutrophyles (activity of microbicidal system of neutrophylic granulocytes, absorbing and digesting potential of microbic bodies). As a consequence of introvenous input of ESS the number of active neutrophyles increased, as well as the amount of bacterias absorbed and digested. The most effective dose was 0,025 mg of silver per kg. Small amounts of ESS efficiently stimulate the microbicidal system of neutrophylic granulocytes, which is shown by the increase of phagocytic activity

Slow light dispersion in coupled periodic waveguides

Periodic waveguides bring a new twist to the typical waveguiding problems of the intermediate case between photonic crystal waveguides and photonic wires or ridge waveguides. We develop an asymptotic theory applicable for a broad class of coupled periodic waveguide structures and use the analytical expressions to identify the generic types of dispersion in the vicinity of a photonic band edge, where the group velocity of light is reduced. We show that the dispersion can be controlled by the longitudinal shift between the waveguides. We also demonstrate through finite-difference time-domain simulations examples of spatial and temporal pulse dynamics in association with different types of slow-light dispersion.This work was supported by the Australian Research Council under the Centres of Excellence Program and through the Australian Partnership for Advanced Computing National Facility (APAC). Part of this project was completed during the visit of A. A. Sukhorukov to McMaster University (Canada) supported by the Australian Academy of Science travel grant. D. N. Chigrin acknowledges partial support by the Deutsche Forschungsgemeinschaft (DFG) through the project FOR 557. A. V. Laurinenko acknowledges partial support from European Commission FP6, project NewTon, NMP4-CT-2005- 017160