Cascaded Nondegenerate Four-Wave Mixing Technique for High-Power Single-Cycle Pulse Synthesis in the Visible and Ultraviolet Ranges

We present a new technique to synthesize high-power single-cycle pulses in the visible and ultraviolet ranges by coherent superposition of a multiband octave-spanning spectrum obtained by highly-nondegenerate cascaded four-wave mixing of femtosecond pulses in bulk isotropic nonresonant media. The generation of coherent spectra spanning over two octaves in bandwidth is experimentally demonstrated using a thin fused silica slide. Full characterization of the intervening multicolored fields using frequency-resolved optical gating, where multiple cascaded orders have been measured simultaneously for the first time, supports the possibility of direct synthesis of near-single-cycle 2.2 fs visible-UV pulses without recurring to complex amplitude or phase control, which should enable many applications in science and technology.Comment: 13 pages, 4 figures. Submitted to Physical Review

Inline self-diffraction dispersion-scan of over octave-spanning pulses in the single-cycle regime

We present an implementation of dispersion-scan based on self-diffraction (SD d-scan) and apply it to the measurement of over octave-spanning sub-4-fs pulses. The results are compared with second-harmonic generation (SHG) d-scan. The efficiency of the SD process is derived theoretically and compared with the spectral response retrieved by the d-scan algorithm. The new SD d-scan has a robust inline setup and enables measuring pulses with over-octave spectra, single-cycle durations and wavelength ranges beyond those of SHG crystals, such as the ultraviolet and the deep-ultraviolet.Comment: 8 pages, 5 figure

Topological superconductivity in lead nanowires

Superconductors with an odd number of bands crossing the Fermi energy have topologically protected Andreev states at interfaces, including Majorana states in one dimensional geometries. Superconductivity, a low number of 1D channels, large spin orbit coupling, and a sizeable Zeeman energy, are present in lead nanowires produced by nanoindentation of a Pb tip on a Pb substrate, in magnetic fields higher than the Pb bulk critical field. A number of such devices have been analyzed. In some of them, the dependence of the critical current on magnetic field, and the Multiple Andreev Reflections observed at finite voltages, are compatible with the existence of topological superconductivity

Modeling of the Sub-Tg Relaxation Spectrum of Pd42.5Ni7.5Cu30P20 Metallic Glass

In this work we study the mechanical relaxation spectrum of Pd42.5Ni7.5Cu30P20 metallic glass. The effect of aging on the relaxation behavior is analyzed by measuring the internal friction during consecutive heating runs. The mechanical relaxation of the wellannealed glass state is modeled by fitting susceptibility functions to the primary and secondary relaxations of the system. The model is able to reproduce the mechanical relaxation spectrum below the glass transition temperature (sub-Tg) in the frequency- temperature ranges relevant for the high temperature physical properties and forming ability of metallic glasses. The model reveals a relaxation spectrum composed by the overlapping of primary and secondary processes covering a wide domain of times but with a relatively narrow range of activation energies.Postprint (author's final draft

The closed-edge structure of graphite and the effect of electrostatic charging

The properties of graphite, and of few-layer graphene, can be strongly influenced by the edge structure of the graphene planes, but there is still much that we do not understand about the geometry and stability of these edges. We present an experimental and theoretical study of the closed edges of graphite crystals, and of the effect of an electric field on their structure. High-resolution transmission electron microscopy is used to image the edge structure of fresh graphite and of graphite that has been exposed to an electric field, which experiences a separation of the graphene layers. Computer simulations based on density functional theory are used to rationalise and quantify the preference for the formation of multiple concentric loops at the edges. A model is also presented to explain how the application of an electric field leads to the separation of the folded edges

The ultraviolet spectrum of HH 24A and its relation to optical spectra

The spectrum of the brightest part (HH 24A) of the complex Herbig-Haro object HH 24 in the short wavelength UV range was studied. The object is of special interest since it is known that in the optical range the continuum is due to dust scattered light originating in a young stellar object while the shock excited emission lines are formed in HH 24A itself. The spectrum shows only a continuum or a quasi-continuum and is not comparable to that of the typical high excitation object like HH1 or HH2 nor to that of a low excitation object like HH3 or HH47

Cryptic species in lichen-forming fungi

This contribution provides a synopsis of the presentations and discussions during the SIG session on cryptic speciation in lichen-forming fungi held during IMC9. In several cases, a re-examination of morphology against the background of molecular phylogenetic evidence revealed, sometimes subtle, morphological and/or chemical characters, supporting the distinction of particular clades at species level. However, there are also examples of cryptic species in which no morphological characters could be identified to distinguish between lineages. Several cases were presented in which distinct lineages are correlated with biogeographical patterns. When and how to name cryptic species was debated, and the use of terms such as “complex” or “aggregate” commended where the taxa formed part of a single lineage