Optimization of high-order harmonic generation by adaptive control of a sub-10-fs pulse wave front

We present a method for the optimization of high-order harmonic generation based on wave-front correction of the driving laser beam. The technique exploits wave-front adaptive control by means of a deformable mirror, governed by an optimization procedure.     

Nonlinear evolution of the lower-hybrid drift instability in a current sheet

The lower-hybrid drift instability is simulated in an ion-scale current sheet using a fully kinetic approach with values of the ion to electron mass ratio up to m(i)/m(e)=1836. Although the instability is localized on the edge of the layer, the nonlinear development increases the electron flow velocity in the central region resulting in a strong bifurcation of the current density and significant anisotropic heating of the electrons. This dramatically enhances the collisionless tearing mode and may lead to the rapid onset of magnetic reconnection for current sheets near the critical scale.     

Accurate sensitivity in optically preamplified direct detection

We present a novel model for calculating the bit error rate in optical communication systems in the case of on-off keying intensity modulation and optically preamplified direct detection. The model accounts for the intersymbol interference and is based on the Laguerre photon-count probability distribution predicted by photodetection theory. For a non-return-to-zero modulation format an accurate value of the sensitivity for a quantum-limited receiver of 33.9 photons/bit is obtained.     

Microwave radiometry of forests

Microwave remote sensing observations provide all weather, day/night monitoring of the earth's surface and make it possible to probe forest vegetation at various depths by operating at different frequencies. Significant progress in microwave radiometry of land surfaces has been made by using advanced airborne and spaceborne instruments and by developing physical and statistical models needed for interpreting the data. At present, a new multi-frequency scanning radiometer, launched in 2002 is providing global observations of the earth's surface at a relatively high resolution, and collected data are currently under study. This paper provides a review of experimental and theoretical investigations carried out in recent years to study the relationships between microwave emission and forest features at regional and global scale. It is shown that, despite the relatively small amount of experimental data currently available, microwave radiometry has proved to be an efficient technique in monitoring forest environments, and in particular in separating forest types, estimating woody biomass and, in some cases, assessing soil surface properties.     

Lateral IBIC characterization of single crystal synthetic diamond detectors

In order to evaluate the charge collection efficiency (CCE) profile of single‐crystal diamond devices based on a p‐type/intrinsic/metal configuration, a lateral Ion Beam Induced Charge (IBIC) analysis was performed over their cleaved cross sections using a 2 MeV proton microbeam. CCE profiles in the depth direction were extracted from the cross‐sectional maps at variable bias voltage. IBIC spectra relevant to the depletion region extending beneath the frontal Schottky electrode show a 100% CCE, with a spectral resolution of about 1.5%. The dependence of the width of the high efficiency region from applied bias voltage allows the constant residual doping concentration of the active region to be evaluated. The region where the electric field is absent shows an exponentially decreasing CCE profile, from which it is possible to estimate the diffusion length of the minority carriers by means of a drift–diffusion model. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Spectral coarse graining and synchronization in oscillator networks

Coarse graining techniques offer a promising alternative to large-scale simulations of complex dynamical systems, as long as the coarse-grained system is truly representative of the initial one. Here, we investigate how the dynamical properties of oscillator networks are affected when some nodes are merged together to form a coarse-grained network. Moreover, we show that there exists a way of grouping nodes preserving as much as possible some crucial aspects of the network dynamics. This coarse graining approach provides a useful method to simplify complex oscillator networks, and more generally, networks whose dynamics involves a Laplacian matrix.     

CW laser-induced photothermal conversion and shape transformation of gold nanodogbones in hydrated chitosan films

We investigate the photothermal conversion and transformation of gold nanoparticles with an initial dogbone shape after dispersion in hydrated chitosan films, which is a representative model of biological tissue, and excitation by a CW diode laser for 1 min. Gold nanodogbones are observed to undergo a distinct modification above a sharp threshold of ~11 W cm⁻² and 110 °C. Surprisingly, the very same modification is achieved up to at least 36 W cm⁻² and 250 °C. We use an analytical model derived from Gans theory to associate the change in color of the films with the change in shape statistics of these gold nanoparticles. This model proves both convenient and dependable. We interpret the photothermal transformation as a rearrangement of particles with a dogbone shape and an aspect ratio of 4.1 into rods with an aspect ratio of 2.5, where material from the end lobes of the dogbones may relocate to the waists of the rods. In turn, additional transitions to stable gold nanospheres may exhibit fairly slower kinetics.     

B-decay CP-asymmetries in SUSY with a U(2)3 flavour symmetry

We study CP asymmetries in rare B decays within supersymmetry with a U(2)³ flavour symmetry, motivated by the SUSY flavour and CP problems, the hierarchies in the Yukawa couplings and the absence so far of any direct evidence for SUSY. Even in the absence of flavour-blind phases, we find potentially sizable CP violating contributions to b→s decay amplitudes. The effects in the mixing-induced CP asymmetries in B→ϕK _S and B→η′K _S , angular CP asymmetries in B→K ^∗ μ ⁺ μ ⁻ and the direct CP asymmetry in B→X _s γ can be in the region to be probed by LHCb and next generation B factories. At the same time, these effects in B decays are compatible with CP violating contributions to meson mixing, including a non-standard B _s mixing phase hinted by current tensions in the CKM fit mostly between S_yKS, e_KS_{\psi K_{S}}, \epsilon_{K} and DM_Bs/DM_Bd\Delta M_{B_{s}}/\Delta M_{B_{d}}.     

One-dimensional photonic crystal design

In this article we present a method to determine the band spectrum, band gaps, and discrete energy levels, of a one-dimensional photonic crystal with localized impurities. For one-dimensional crystals with piecewise constant refractive indices we develop an algorithm to recover the refractive index distribution from the period map. Finally, we derive the relationship between the period map and the scattering matrix containing the information on the localized modes.