Self-guiding of infrared and visible light in photonic crystal slabs

We experimentally demonstrate diffractionless guidance and efficient routing of light in two-dimensional photonic crystal slabs at infrared and visible wavelengths. Our particular design allows for simultaneous guidance of TE and TM polarized light beams at the same wavelength. Routing performance and possibilities of propagation loss reduction are investigated experimentally. Experimental results are in excellent agreement with three-dimensional simulations.     

Effects of anisotropic disorder in an optical metamaterial

We consider the effect of disorder in one transverse dimension, termed anisotropic disorder, on the optical properties of a metamaterial consisting of cut-wire-pair meta-atoms. The work comprises experimental and numerical studies. The appropriate samples were fabricated and their optical properties quantified in the far-field. For comparison large-scale rigorous numerical simulations were performed. We observe excellent agreement between experiment and theory. Based on our results we reveal how the electric dipole interactions between adjacent meta-atoms affect the overall spectral response of the metamaterial. Our main observation is a polarization-sensitive degradation of the symmetric resonance for anisotropic disorder.     

Tuning Electron Donor–Acceptor Hybrids by Alkali Metal Complexation

A zinc phthalocyanine endowed with four [18]‐crown‐6 moieties, ZnPc_TeCr, has been prepared and self‐assembled with either pyridyl‐functionalized perylenebisimides (PDI‐Py) or fullerenes (C₆₀‐Py) to afford a set of novel electron donor–acceptor hybrids. In the case of ZnPc_TeCr, aggregation has been circumvented by the addition of potassium or rubidium ions to lead to the formation of monomers and cofacial dimers, respectively. From fluorescence titration experiments, which gave rise to mutual interactions between the electron donors and the acceptors in the excited state, the association constants of the respective ZnPc_TeCr monomers and/or dimers with the corresponding electron acceptors were derived. Complementary transient‐absorption experiments not only corroborated photoinduced electron transfer from ZnPc_TeCr to either PDI‐Py or C₆₀‐Py within the electron donor–acceptor hybrids, but also the unexpected photoinduced electron transfer within ZnPc_TeCr dimers. In the electron donor–acceptor hybrids, the charge‐separated‐state lifetimes were elucidated to be close to 337 ps and 3.4 ns for the two PDI‐Pys, whereas the longest lifetime for the photoactive system that contains C₆₀‐Py was calculated to be approximately 5.1 ns.     

Spatiotemporal discrete Ginzburg-Landau solitons in two-dimensional photonic lattices

In the framework of the continuous-discrete cubic-quintic Ginzburg-Landau model, spatiotemporal dissipative solitons which are highly confined inside two-dimensional photonic lattices are found numerically. The domains of existence in the relevant parameter space, of in-phase (unstaggered) on-site (single-peaked), inter-site (double-peaked), and flat-top-like (four-peaked) spatiotemporal dissipative solitons are determined. We show that the on-site solitons are stable in the whole domain of their existence and we find the stability domains of both inter-site and flat-top-like solitons. We describe the complex instability-induced scenarios of the dynamics of spatiotemporal discrete Ginzburg-Landau solitons in two-dimensional photonic lattices.     

Analytical relation between effective mode field area and waveguide dispersion in microstructure fibers

For optical fibers exhibiting a radially symmetric refractive index profile, there exists an analytical relation that connects waveguide dispersion and the Petermann-II mode field radius. We extend the usefulness of this relation to the nonradially symmetric case of microstructure fibers in the anomalous dispersion regime, yielding a simple relation between dispersion and effective mode field area. Assuming a Gaussian mode distribution, we derive a fundamental upper limit for the effective mode field area that is required to obtain a certain amount of anomalous waveguide dispersion. This relation is demonstrated to show excellent agreement for fiber designs suited for supercontinuum generation and soliton lasers in the near infrared.     

Observation of two-dimensional lattice interface solitons

We report on the experimental observation of two-dimensional solitons at the interface between square and hexagonal waveguide arrays. In addition to the different symmetries of the lattices, the influence of a varying refractive index modulation depth is investigated. Such variation strongly affects the properties of surface solitons residing at different sides of the interface.     

Field emission through atoms chemisorbed on a metal surface

An exact general expression for the field emission current is derived under two alternative forms in the frame of a new formalism of tunnelling developed in preceding articles. This formalism is applied to study qualitatively the TED (total energy distribution) in the presence of a chemisorbed atom. It is shown in particular that the overlap between the atomic electronic state and the continuum of states of the vacuum induces, in the high-field regime, a non-negligible variation of the position and width of the resonance peak with the electric field.     

Isolement et structure d'un nouveau diterpène: L'acide daniellique Stéréochimie de l'acide daniellique

A new diterpene acid, daniellic acid, has been isolated from the African copal tree, Daniellia oliveri (Caesalpineae). Structure (I) is demonstrated for daniellic acid; the stereochemistry implied (relative and absolute) is derived from a correlation with agathic acid.