Nonlinear soliton matching between optical fibers

In this Letter, we propose a generic nonlinear coupling coefficient, η(NL)2=η|γ/β?|(fiber2)/|γ/β?|(fiber1), which gives a quantitative measure for the efficiency of nonlinear matching of optical fibers by describing how a fundamental soliton couples from one fiber into another. Specifically, we use η(NL) to demonstrate a significant soliton self-frequency shift of a fundamental soliton, and we show that nonlinear matching can take precedence over linear mode matching. The nonlinear coupling coefficient depends on both the dispersion (β?) and nonlinearity (γ), as well as on the power coupling efficiency η. Being generic, η(NL) enables engineering of general waveguide systems, e.g., for optimized Raman redshift or supercontinuum generation.     

Slow-light enhanced correlated photon pair generation in a silicon photonic crystal waveguide

We report the generation of correlated photon pairs in the telecom C-band at room temperature from a dispersion-engineered silicon photonic crystal waveguide. The spontaneous four-wave mixing process producing the photon pairs is enhanced by slow-light propagation enabling an active device length of less than 100?μm. With a coincidence to accidental ratio of 12.8 at a pair generation rate of 0.006 per pulse, this ultracompact photon pair source paves the way toward scalable quantum information processing realized on-chip.     

Plasmonic rod dimers as elementary planar chiral meta-atoms

We theoretically calculate the electromagnetic response of metallic rod dimers for the arbitrary planar arrangement of rods in the dimer. It is shown that dimers without an in-plane symmetry axis exhibit elliptical dichroism and act as "atoms" in planar chiral metamaterials. Because of a very simple geometry of the rod dimer, such planar metamaterials are much easier to fabricate than conventional split-ring or gammadion-type structures and lend themselves to a simple analytical treatment based on a coupled dipole model. Dependencies of the metamaterial's directional asymmetry on the dimer's geometry are established analytically and confirmed in numerical simulations.     

High-speed modal decomposition of mode instabilities in high-power fiber lasers

A high-speed mode analysis technique is required to gain fundamental understanding of mode instabilities in high-power fiber laser systems. In this work a technique, purely based on the intensity profile of the beam, is demonstrated to be ideally suited to analyze fiber laser dynamics. This technique, together with a high-speed camera, has been applied to the study of the temporal dynamics of mode instabilities at high average powers with up to 20,000 frames per second. These measurements confirm that energy transfer between the fluctuating transversal modes takes place in millisecond-time-scale.     

Holoscopy--holographic optical coherence tomography

Scanning optical coherence tomography (OCT) is limited in sensitivity and resolution by the restricted focal depth of the confocal detection scheme. Holoscopy, a combination of holography and Fourier-domain full-field OCT, is proposed as a way to detect photons from all depths of a sample volume simultaneously with uniform sensitivity and lateral resolution, even at high NAs. By using the scalar diffraction theory, as frequently applied in digital holographic imaging, we fully reconstruct the object field with depth-invariant imaging quality. In vivo imaging of human skin is demonstrated with an image quality comparable to conventionally scanned OCT.     

Apatite type lanthanum silicate and composite anode half cells

Apatite type rare earth silicates are being extensively studied as electrolyte material for intermediate temperature solid oxide fuel cells (SOFC). In this paper we presents results on synthesis of Al and/or Fe-doped ATLS, the design of compatible anode materials, thermal expansion properties and co-sintering of half-cells from expansion matched materials using the advanced pulsed electric current sintering (PECS) technique. The issues related to the co-sintering of half cells have been addressed successfully by the combined use of nano powders and PECS.     

High-order harmonic generation enhanced by XUV light

The combination of high-order harmonic generation (HHG) with resonant XUV excitation of a core electron into the transient valence vacancy that is created in the course of the HHG process is investigated theoretically. In this setup, the first electron performs a HHG three-step process, whereas the second electron Rabi flops between the core and the valence vacancy. The modified HHG spectrum due to recombination with the valence and the core is determined and analyzed for krypton on the 3d→4p resonance in the ion. We assume an 800?nm laser with an intensity of about 10(14)?W/cm2 and XUV radiation from the Free Electron Laser in Hamburg (FLASH) with an intensity in the range 10(13)-10(16)W cm2. Our prediction opens perspectives for nonlinear XUV physics, attosecond x rays, and HHG-based spectroscopy involving core orbitals.     

Thermal stability of the cubic phase in Ba0.5Sr0.5Co0.8Fe0.2O3 - δ (BSCF)1

Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3 - δ (BSCF) is a material with excellent oxygen ionic and electronic transport properties reported by many research groups. In its cubic phase, this mixed ionic-electronic conducting (MIEC) perovskite is a promising candidate for oxygen permeation membranes. For this application, its long-term stability under operating conditions (especially temperature and oxygen partial pressure) is of crucial importance.The present work is focused on the thermal stability of the BSCF cubic phase in the targeted temperature range for applications (700…900 °C) in light of previous studies in literature reporting a reversible transition to a hexagonal phase somewhere below 900 °C.To this end, single phase cubic BSCF powders were annealed at different temperatures over varying periods of time. Phase composition was subsequently analysed by X-ray diffractometry (XRD) in order to determine both the temperature limit and the time-scale for the formation of the hexagonal phase. Additionally, the long-term behaviour of the electrical conductivity was examined on bulk samples at 700 °C, 800 °C and 900 °C over several hundreds of hours, showing a prolonged decrease at 800 °C. The decrease in electrical conductivity at this temperature was also examined on bulk samples with different grain sizes, showing a more pronounced decrease the smaller the average grain size.Coexistence of both phases (cubic and hexagonal) could also be shown for 700 °C, however with a different phase equilibrium than at 800 °C.     

Structure factor of ferrofluids with chain aggregates: Theory and computer simulations

In this paper we present theoretical and simulation results on the structure factor of mono- and bidisperse ferrofluids with chain aggregates, both with and without an applied external magnetic field. Chain distribution is obtained by the density functional theory (DFT). The radial distribution function (RDF) is calculated directly on the basis of the chain distribution and Fourier transformed to calculate the structure factor. An extensive comparison of the theoretical predictions to the results of the molecular dynamics computer simulations is provided. The proposed combined approach allows to elucidate the connection between experimentally observed small angle neutron scattering (SANS) images and the ferrofluid microstructure.