Numerical characterization of high harmonic attosecond pulses

A numerical simulation of attosecond harmonic pulse generation in a three-dimensional field-ionizing gas is presented. Calculated harmonic efficiencies quantitatively reproduce experimental findings. This allows a quantitative characterization of attosecond pulse generation revealing information currently not accessible by experiment. The rapid phase variation and spatiotemporal distortions of harmonics are smaller than anticipated, allowing focusing of 30-nm, 750-as pulses to intensities in excess of 10(13) W/cm(2). Feasibility of such pulses brings novel applications such as extreme ultraviolet nonlinear optics and attosecond pump probe spectroscopy within reach.     

X-ray determination of the mean amplitudes of vibration and debye temperatures of some rare earth monochalcogenides

The x-ray diffraction intensities of Bragg reflections have been measured at room temperature for thulium selenide, samarium sulphide, samarium selenide and samarium telluride. On the basis of a common amplitude approximation, the Debye-Waller factor, the mean amplitude of vibration and the Debye temperature have been evaluated. The values of the Debye temperatures and mean amplitudes of vibration are 176±16°K, 0·185 ± 0·017 Å (TmSe), 155 ± 7°K, 0·244 ± 0·012 Å (SmS), 153 ± 14°K, 0·221 ± 0·020 Å (SmSe) and 151 ± 20°K, 0·204 ± 0·027 Å (SmTe).     

Optical pulse compression: bulk media versus hollow waveguides

Optical pulse-compression systems based on bulk materials and hollow waveguides are compared by use of coupled-mode theory. Our analysis reveals an intuitive picture of the temporal and spatial nonlinear processes involved in pulse compression. Further, simple formulas are derived that give an estimate of the spatial distortions and of the self-phase modulation induced by Kerr nonlinearity. Finally, a parameter regime is identified in which self-focusing in bulk media is suppressed, resulting in a substantial improvement in the spatial beam quality of the compressed pulses.     

Sub-leading flow modes in PbPb collisions at sNN = 2.76 TeV from the HYDJET++ model

Recent LHC results on the appearance of sub-leading flow modes in PbPb collisions at 2.76 TeV, related to initial-state fluctuations, are analyzed and interpreted within the HYDJET++ model. Using the newly introduced Principal Component Analysis (PCA) method applied to two-particle azimuthal correlations extracted from the model calculations, the leading and sub-leading flow modes are studied as a function of the transverse momentum (p_T) over a wide centrality range. The leading modes of the elliptic (v₂⁽¹⁾) and triangular (v₃⁽¹⁾) flow calculated with the HYDJET++ model reproduce rather well the v₂{2} and v₃{2} coefficients measured experimentally using the two-particle correlations. Within the p_T ≤ 3 GeV/c range, where hydrodynamics dominates, the sub-leading flow effects are greatest at the highest p_T of around 3 GeV/c. The sub-leading elliptic flow mode (v₂⁽²⁾), which corresponds to the n = 2 harmonic, has a small non-zero value and slowly increases from central to peripheral collisions, while the sub-leading triangular flow mode (v₃⁽²⁾), which corresponds to the n = 3 harmonic, is even smaller and does not depend on centrality. For n = 2, the relative magnitude of the effect measured with respect to the leading flow mode shows a shallow minimum for semi-central collisions and increases for very central and for peripheral collisions. For the n = 3 case, there is no centrality dependence. The sub-leading flow mode results obtained from the HYDJET++ model are in rather good agreement with the experimental measurements of the CMS Collaboration.     

Electron Single and Double-slit Diffraction in the Temporal Domain

Few-cycle pulses with stable and controllable relative phase between the carrier wave and the envelope （CE phase） have become available as research tools. The actual shape of the electric field of such a pulse strongly depends on this phase, and so do the physical processes the pulse generates. Owing to its pronounced nonlinearity, above-threshold ionization （ATI） provides an excellent example. In particular, the rescattering-induced high- energy part of the ATI spectrum exhibits a dramatic dependence on the value of the CE phase. Moreover, the backward/forward symmetry of the ATI spectrum generated by a, long pulse is broken by a few-cycle pulse. Therefore, analyzing the spectrum in two opposite directions provides a very accurate means of measuring the CE phase.     

Viologen‐Templated Arrays of Cucurbit[7]uril‐Modified Iron‐Oxide Nanoparticles

Magnetic and fluorescent assemblies of iron‐oxide nanoparticles (NPs) were constructed by threading a viologen‐based ditopic ligand, DPV²⁺, into the cavity of cucurbituril (CB[7]) macrocycles adsorbed on the surface of the NPs. Evidence for the formation of 1:2 inclusion complexes that involve DPV²⁺ and two CB[7] macrocycles was first obtained in solution by ¹H NMR and emission spectroscopy. DPV²⁺ was found to induce self‐assembly of nanoparticle arrays (DPV²⁺?CB[7]NPs) by bridging CB[7] molecules on different NPs. The resulting viologen‐crosslinked iron‐oxide nanoparticles exhibited increased saturation magnetization and emission properties. This facile supramolecular approach to NP self‐assembly provides a platform for the synthesis of smart and innovative materials that can achieve a high degree of functionality and complexity and that are needed for a wide range of applications.