Fano-resonant mechanism of terajet formation using graphene-covered high-index mesoscale spheres.

Photonic jet in terahertz (THz) frequency range (terajet) plays an important role in modern THz scanning systems to achieve a superresolution beyond the diffraction limit. Based on analytical simulations, we introduce a synergetic effect of a mesoscale dielectric sphere and graphene to improve the focusing properties of a particle. We show that a graphene-covered dielectric sphere is able to enhance the field behind it if the refractive index is high. This conflicts with a generally accepted statement that a jet is generated only for low-index dielectrics with n < 2. We demonstrate the tunability of the terajet characteristics with respect to the graphene Fermi energy and discover a Fano resonance causing the field increase. This design leverages the tuning properties of the graphene allowing dynamic control over the power and size of the generated terajet in real time. With high-index materials, we get the opportunity for integration of terajet-assisted imaging with semiconductor technology.

Optical waveguide mode control by nanoslit-enhanced terahertz field.

In this Letter we propose a scheme providing control over an optical waveguide mode by a terahertz (THz) wave. The scheme is based on an optimization of the overlap between the optical waveguide mode and the THz field, with the THz field strength enhanced by the presence of a metallic nanoslit surrounding the waveguide. We find an optimum balance between the optical mode attenuation and Kerr-induced change in the propagation constant. The criterion for a π/2-cumulative phase shift, for instance for application in a Mach-Zehnder interferometer configuration, requires 10 kV/cm THz field, which in turn is estimated to result in a nonlinear change of the refractive index in the waveguide of 0.001. Our simulations prove that it is quite reasonable to observe the effect experimentally.

The evolutionary relationships of two families of cottoid fishes of Lake Baikal (east Siberia) as suggested by analysis of mitochondrial DNA.

Fragments of mtDNA genes Cyt B, ATPase 6, and ATPase 8 of six cottoid fishes species of Lake Baikal (East Siberia) were amplified and sequenced. In addition mtDNAs of the same fish were subjected to restriction analysis. The data obtained were used to construct phylogenetic trees. The topology of the ATPase tree differs from those of the Res (restriction) and Cyt B trees. Clustering of species within the trees confirms the viewpoint of Taliev (1955, Baicalian Sculpins (Cottoidei)) according to which Baikalian cottoids originate from two ancestral forms. The times of branching obtained do not confirm the existing viewpoint according to which the two golomyankas (Comephorus baicalensis and Comephorus dybowskii) are pre-Baikal (Myocene) relicts: these two species may have originated 1.2-1.8 million years ago in Baikal, and they seem to represent an example of rapid morphological evolution which resulted in the formation of a new family.