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Single dielectric microspheres can manipulate light focusing and collection to enhance optical interaction with surfaces. To demonstrate this principle, we experimentally investigate the enhancement of the Raman signal collected by a single dielectric microsphere, with a radius much larger than the exciting laser spot size, residing on the sample surface. The absolute microsphere-assisted Raman signal from a single graphene layer measured in air is more than a factor of two higher than that obtained with a high numerical aperture objective. Results from Mie’s theory are used to benchmark numerical simulations and an analytical model to describe the isolated microsphere focusing properties. The analytical model and the numerical simulations justify the Raman signal enhancement measured in the microsphere-assisted Raman spectroscopy experiments.

Mott transitions in real materials are first order and almost always associated with lattice distortions, both features promoting the emergence of nanotextured phases. This nanoscale self-organization creates spatially inhomogeneous regions, which can host and protect transient non-thermal electronic and lattice states triggered by light excitation. However, to gain full control of the Mott transition for potential applications in the field of ultrafast switching and neuromorphic computing it is necessary to develop novel spatial and temporal multiscale experimental probes as well as theoretical approaches able to distill the complex microscopic physics into a coarse-grained modelling. Here, we combine time-resolved X-ray microscopy, which snaps phase transformations on picosecond timescales with nanometric resolution, with a Landau-Ginzburg functional approach for calculating the strain and electronic real-space configurations. We investigate V2O3, the archetypal Mott insulator in which nanoscale self-organization already exists in the low-temperature monoclinic phase and strongly affects the transition towards the high-temperature corundum metallic phase. Our joint experimental-theoretical approach uncovers a remarkable out-of-equilibrium phenomenon: the photoinduced stabilisation of the long sought monoclinic metal phase, which is absent at equilibrium and in homogeneous materials, but emerges as a metastable state solely when light excitation is combined with the underlying nanotexture of the monoclinic lattice. Our results provide full comprehension of the nanotexture dynamics across the insulator-to-metal transition, which can be readily extended to many families of Mott insulating materials. The combination of ultrafast light excitation and spatial nanotexture turns out to be key to develop novel control protocols in correlated quantum materials.

The insulator-to-metal transition in Mott insulators is the key mechanism for a novel class of electronic devices, belonging to the Mottronics family. Intense research efforts are currently devoted to the development of specific control protocols, usually based on the application of voltage, strain, pressure and light excitation. The ultimate goal is to achieve the complete control of the electronic phase transformation, with dramatic impact on the performance, for example, of resistive switching devices. Here, we investigate the simultaneous effect of external voltage and excitation by ultrashort light pulses on a single Mottronic device based on a V$_2$O$_3$ epitaxial thin film. The experimental results, supported by finite-element simulations of the thermal problem, demonstrate that the combination of light excitation and external electrical bias drives a volatile resistivity drop which goes beyond the combined effect of laser and Joule heating. Our results impact on the development of protocols for the non-thermal control of the resistive switching transition in correlated materials.

International audience; Time-effective, unsupervised clustering techniques are exploited to discriminate nanometric metal disks patterned on a dielectric substrate. The discrimination relies on cluster analysis applied to time-resolved optical traces obtained from thermo-acoustic microscopy based on asynchronous optical sampling. The analysis aims to recognize similarities among nanopatterned disks and to cluster them accordingly. Each cluster is characterized by a fingerprint time-resolved trace, synthesizing the common features of the thermo-acoustics response of the composing elements. The protocol is robust and widely applicable, not relying on any specific knowledge of the physical mechanisms involved. The present route constitutes an alternative diagnostic tool for on-chip non-destructive testing of individual nano-objects.

The thermo-mechanical properties of streptavidin-conjugated gold nanospheres, adhered to a surface via complex molecular chains, are investigated by two-color infrared asynchronous optical sampling pump-probe spectroscopy. Nanospheres with different surface densities have been deposited and exposed to a plasma treatment to modify their polymer binding chains. The aim is to monitor their optical response in complex chemical environments that may be experienced in, e.g., photothermal therapy or drug delivery applications. By applying unsupervised learning techniques to the spectroscopic traces, we identify their thermo-mechanical response variation. This variation discriminates nanospheres in different chemical environments or different surface densities. Such discrimination is not evident based on a standard analysis of the spectroscopic traces. This kind of analysis is important, given the widespread application of conjugated gold nanospheres in medicine and biology.

Internal feeding is considered to shield sessile herbivorous insects from exposure to nonsystemic insecticides aerially sprayed against forest defoliators, although this has not been tested. It is, however, established that leaf damage caused by defoliators affects the survivorship and oviposition behavior of sessile herbivores. Thus feeding ecology and competition may mediate nontarget effects of insecticides on these insects. We tested the ecological sensitivity of 3 guilds of sessile herbivores (upper-surface leaf-miners, lower-surface leaf-miners, and gall-inducers) to the lipophilic larvicides diflubenzuron and tebufenozide aerially applied either at operational rates (12 g active ingredient [a.i.]/ha and 69.6 g [a.i.]/ha, respectively) or at maximum legal rates (60 g [a.i.]/ha and 180 g [a.i.]/ha, respectively), in German oak forests. Diflubenzuron affected leaf-miners at different life stages depending on their position on the leaf but had no effect on gall-inducers. Tebufenozide showed a similar, but not significant, pattern in leaf-miners and did not affect gall-inducers. By reducing the incidence of chewing damage on leaves, both insecticides offset the negative effect of competition on leaf-miner and gall-inducers. The net outcome of insecticide treatment was positive for guilds avoiding exposure, but negative for upper-surface leaf-miners. Exposure to insecticides in situ can be mediated by subtle differences in species biology and species interactions, with potential implications for organisms usually considered safe in risk assessment studies. Environ Toxicol Chem 2021;00:1-17. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

International audience; The full control of the fundamental photophysics of nanosystems at frequencies as high as few THz is key for tunable and ultrafast nanophotonic devices and metamaterials. Here we combine geometrical and ultrafast control of the optical properties of halide perovskite nanoparticles, which constitute a prominent platform for nanophotonics. The pulsed photoinjection of free carriers across the semiconducting gap leads to a subpicosecond modification of the far-field electromagnetic properties that is fully controlled by the geometry of the system. When the nanoparticle size is tuned so as to achieve the overlap between the narrowband excitons and the geometry-controlled Mie resonances, the ultrafast modulation of the transmittivity is completely reversed with respect to what is usually observed in nanoparticles with different sizes, in bulk systems, and in thin films. The interplay between chemical, geometrical, and ultrafast tuning offers an additional control parameter with impact on nanoantennas and ultrafast optical switches.

It is shown that the Raman signal can be enhanced using BaTiO 3 microspheres beyond that obtained by the highest numerical aperture objective available on a standard Raman microscope. This research is aimed at understanding the basis of the light interaction at the nanoscale level, with implications for photodynamic processes on bio-objects.

The influence of Mott physics on the doping–temperature phase diagram of copper oxides represents a major issue that is the subject of intense theoretical and experimental efforts. Here, we investigate the ultrafast electron dynamics in prototypical single-layer Bi-based cuprates at the energy scale of the O-2p → Cu-3d charge-transfer (CT) process. We demonstrate a clear evolution of the CT excitations from incoherent and localized, as in a Mott insulator, to coherent and delocalized, as in a conventional metal. This reorganization of the high-energy degrees of freedom occurs at the critical doping pcr ≈ 0.16 irrespective of the temperature, and it can be well described by dynamical mean-field theory calculations. We argue that the onset of low-temperature charge instabilities is the low-energy manifestation of the underlying Mottness that characterizes the p < pcr region of the phase diagram. This discovery sets a new framework for theories of charge order and low-temperature phases in underdoped copper oxides. The electron dynamics of single-layer Bi2Sr2−xLaxCuO6+δ is studied as a function of doping, revealing the evolution of charge-transfer excitations from incoherent and localized (as in a Mott insulator) to coherent and delocalized (as in a conventional metal).

Traditionally, dynamic atomic force microscopy (AFM) techniques are based on the analysis of the quasi-steady state response of the cantilever deflection in terms of Fourier analysis. Here we describe a technique that instead exploits the often disregarded transient response of the cantilever through a relatively modern mathematical tool, which has caused important developments in several scientific fields but that is still quite unknown in the AFM context: the wavelet analysis. This tool allows us to localize the time-varying spectral composition of the initial oscillations of the cantilever deflection when an impulsive excitation is given (as in the band excitation method), a mode that we call the few-cycle regime. We show that this regime encodes very meaningful information about the tip-sample interaction in a unique and extremely sensitive manner. We exploit this high sensitivity to gain detailed insight into multiple physical parameters that perturb the dynamics of the AFM probe, such as the tip radius, Hamaker constant, sample’s elastic modulus and height of an adsorbed water layer. We validate these findings with experimental evidence and computational simulations and show a feasible path towards the simultaneous retrieval of multiple physical parameters.

Unveiling the physics that governs the intertwining between the nanoscale self-organization and the dynamics of insulator-to-metal transitions (IMTs) is key for controlling on demand the ultrafast switching in strongly correlated materials and nanodevices. A paradigmatic case is the IMT in ${\mathrm{V}}_{2}{\mathrm{O}}_{3}$, for which the mechanism that leads to the nucleation and growth of metallic nanodroplets out of the supposedly homogeneous Mott insulating phase is still a mystery. Here, we combine x-ray photoemission electron microscopy and ultrafast nonequilibrium optical spectroscopy to investigate the early-stage dynamics of isolated metallic nanodroplets across the IMT in ${\mathrm{V}}_{2}{\mathrm{O}}_{3}$ thin films. Our experiments show that the low-temperature monoclinic antiferromagnetic insulating phase is characterized by the spontaneous formation of striped polydomains, with different lattice distortions. The insulating domain boundaries accommodate the birth of metallic nanodroplets, whose nonequilibrium expansion can be triggered by the photoinduced change of the $3d$-orbital occupation. We address the relation between the spontaneous nanotexture of the Mott insulating phase in ${\mathrm{V}}_{2}{\mathrm{O}}_{3}$ and the timescale of the metallic seeds growth. We speculate that the photoinduced metallic growth can proceed along a nonthermal pathway in which the monoclinic lattice symmetry of the insulating phase is partially retained.

A new paradigm for active nanophotonic structures and metadevices based on perovskites has recently emerged due to several unique features of these materials such as room-temperature exciton, tunable bandgap energy, and low-cost fabrication methods [1,2]. Progress towards future applications requiring dynamical control of the optical response will depend on our understanding of photoexcitations in these systems [3,4]. In this work, we report the first experimental observation of ultrafast all-optical modulation of Fano resonant halide perovskite nanoparticles (NP). Our measurements, corroborated by analytical and numerical models, show that the out-of-equilibrium dynamics of these systems can be thoroughly controlled by engineering the NP size.

Multiorbital correlated materials are often on the verge of multiple electronic phases (metallic, insulating, superconducting, charge and orbitally ordered), which can be explored and controlled by small changes of the external parameters. The use of ultrashort light pulses as a mean to transiently modify the band population is leading to fundamentally new results. In this paper we will review recent advances in the field and we will discuss the possibility of manipulating the orbital polarization in correlated multi-band solid state systems. This technique can provide new understanding of the ground state properties of many interesting classes of quantum materials and offers a new tool to induce transient emergent properties with no counterpart at equilibrium. We will address: the discovery of high-energy Mottness in superconducting copper oxides and its impact on our understanding of the cuprate phase diagram; the instability of the Mott insulating phase in photoexcited vanadium oxides; the manipulation of orbital-selective correlations in iron-based superconductors; the pumping of local electronic excitons and the consequent transient effective quasiparticle cooling in alkali-doped fullerides. Finally, we will discuss a novel route to manipulate the orbital polarization in a a k-resolved fashion. © 2018 COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only.

Signals consisting of multiple frequencies and changing their amplitude while propagating in time generate in many experiments. The analysis of such signals requires special methodological approach and mathematical apparatus, which allows ascertain the main features of the signal by a signal transformation. The general method is to apply Fourier transform analysis. However, Fourier transform analysis provides actual spectra for stationary signals alone. For signals changing their characteristics over time the method of analysis that presents the signal changes in both time and frequency is required, and one of the most valid methods is wavelet transform. The present work is aimed to show the advantages of wavelet transform in comparison with FT, when signals changing their characteristics over time is necessary to investigate.

The aim of the data analysis is to explore the main characteristics of the signal by a signal transformation. The most commonly used way of analyzing the signals is the Fourier transform (FT). For stationary systems, where the signal properties over time do not change, the FT spectrum is easily interpreted. However, in cases where the systems change their physical properties and hence their characteristic spectrum in time, FT shows only the spectrum integrated over the acquisition time. As a consequence the modifications of the temporal signal are not directly correlated with the frequency features of the spectrum. For such non-stationary signals the method that combines the time and frequency domain analysis and hence shows the signal evolution in both time and frequency is needed. The windowed FT belongs to the family of techniques with such temporal and spectral resolution and it has been one of the first methods devised to operate in the time-frequency plane. However, windowed FT has the drawback of the fixed time-frequency resolution, because after the choice of a window function, the size of the time-frequency window is fixed. In contrary, the wavelet transform (WT) is a mathematical approach that gives the time-frequency representation of a signal with the possibility to adjust the time-frequency resolution, hence, WT may be considered as the time-frequency analysis method with an adjustable window, which is an improved alternative to the windowed FT. In the article, the advantages of WT in comparison with FT analysis are illustrated.

© 2017 American Chemical Society. Ultrathin metal nanoparticles coatings, synthesized by gas-phase deposition, are emerging as go-to materials in a variety of fields ranging from pathogens control and sensing to energy storage. Predicting their morphology and mechanical properties beyond a trial-and-error approach is a crucial issue limiting their exploitation in real-life applications. The morphology and mechanical properties of Ag nanoparticle ultrathin films, synthesized by supersonic cluster beam deposition, are here assessed adopting a bottom-up, multitechnique approach. A virtual film model is proposed merging high resolution scanning transmission electron microscopy, supersonic cluster beam dynamics, and molecular dynamics simulations. The model is validated against mechanical nanometrology measurements and is readily extendable to metals other than Ag. The virtual film is shown to be a flexible and reliable predictive tool to access morphology-dependent properties such as mesoscale gas-dynamics and elasticity of ultrathin films synthesized by gas-phase deposition. ispartof: Journal of Physical Chemistry C vol:121 issue:40 pages:22434-22441 status: published

In the synthesis of nanostructures by pulsed laser deposition (PLD), a crucial role is played by the environmental deposition pressure and the substrate temperature. Due to the high temperature of nanoparticles (NPs) at landing, other factors may determine the structure of the resulting aggregates. Here, Au and TiO2 nanostructures are obtained by non-thermal fs-PLD in ambient conditions. On Si(100), only TiO2 NPs form fractals with areas up to ~ 1 × 106 nm2, while on quartz Au NPs also form fractals with areas up to ~ 5 × 103 nm2, a much smaller size with respect to the TiO2 case. The aggregation is described by a simple diffusive model, taking into account isotropic diffusion of the NPs, allowing quantitative simulations of the NPs and fractal area. The results highlight the key role of substrate thermal conductivity in determining the formation of fractals. [Figure not available: see fulltext.].

The Thermal Boundary Resistance at the interface between a nanosized Al film and an Al_{2}O_{3} substrate is investigated at an atomistic level. A room temperature value of 1.4 m^{2}K/GW is found. The thermal dynamics occurring in time-resolved thermo-reflectance experiments is then modelled via macro-physics equations upon insertion of the materials parameters obtained from atomistic simulations. Electrons and phonons non-equilibrium and spatio-temporal temperatures inhomo- geneities are found to persist up to the nanosecond time scale. These results question the validity of the commonly adopted lumped thermal capacitance model in interpreting transient nanocalorimetry experiments. The strategy adopted in the literature to extract the Thermal Boundary Resistance from transient reflectivity traces is revised at the light of the present findings. The results are of relevance beyond the specific system, the physical picture being general and readily extendable to other heterojunctions., 12 pages, 8 figures

One-color transient reflectivity measurements are carried out on two different samples of vertically aligned single-wall carbon nanotube bundles and compared with the response recently published on unaligned bundles. The negative sign of the optical response for both samples indicates that the free electron character revealed on unaligned bundles is only due to the intertube interactions favored by the tube bending. Neither the presence of bundles nor the existence of structural defects in aligned bundles is able to induce a free-electron like behavior of the photoexcited carriers. This result is also confirmed by the presence of non-linear excitonic effects in the transient response of the aligned bundles. (C) 2013 Elsevier B.V. All rights reserved.

High-resolution time resolved transmittivity measurements on horizontally aligned free-standing multi-walled carbon nanotubes reveal a different electronic transient behavior from that of graphite. This difference is ascribed to the presence of discrete energy states in the multishell carbon nanotube electronic structure. Probe polarization dependence suggests that the optical transitions involve definite selection rules. The origin of these states is discussed and a rate equation model is proposed to rationalize our findings.

We use time- and energy-resolved optical spectroscopy to investigate the coupling of electron-hole excitations to the magnetic environment in the relativistic Mott insulator Na$_2$IrO$_3$. We show that, on the picosecond timescale, the photoinjected electron-hole pairs delocalize on the hexagons of the Ir lattice via the formation of quasi-molecular orbital (QMO) excitations and the exchange of energy with the short-range-ordered zig-zag magnetic background. The possibility of mapping the magnetic dynamics, which is characterized by typical frequencies in the THz range, onto high-energy (1-2 eV) charge excitations provides a new platform to investigate, and possibly control, the dynamics of magnetic interactions in correlated materials with strong spin-orbit coupling, even in the presence of complex magnetic phases., 5 pages, 4 figures, supplementary information

The possibility of investigating the dynamics of solids on timescales faster than the thermalization of the internal degrees of freedom has disclosed novel non-equilibrium phenomena that have no counterpart at equilibrium. Transition metal oxides (TMOs) provide an interesting playground in which the correlations among the charges in the metal $d$-orbitals give rise to a wealth of intriguing electronic and thermodynamic properties involving the spin, charge, lattice and orbital orders. Furthermore, the physical properties of TMOs can be engineered at the atomic level, thus providing the platform to investigate the transport phenomena on timescales of the order of the intrinsic decoherence time of the charge excitations. Here, we review and discuss three paradigmatic examples of transient emerging properties that are expected to open new fields of research: i) the creation of non-thermal magnetic states in spin-orbit Mott insulators; ii) the possible exploitation of quantum paths for the transport and collection of charge excitations in TMO-based few-monolayers devices; iii) the transient wave-like behavior of the temperature field in strongly anisotropic TMOs., Comment: 39 pages, 7 figures

The specific mechanisms which leads to the formation of fractal nanostructures by pulsed laser deposition remain elusive despite intense research efforts, motivated mainly by the technological interest in obtaining tailored nanostructures with simple and scalable production methods. Here we focus on fractal nanostructures of titanium dioxide, $TiO_2$, a strategic material for many applications, obtained by femtosecond laser ablation at ambient conditions. We model the fractal formation through extensive Monte Carlo simulations based on a set of minimal assumptions: irreversible sticking and size independent diffusion. Our model is able to reproduce the fractal dimensions and the area distributions of the nanostructures obtained in the experiments for different densities of the ablated material. The comparison of theory and experiment show that such fractal aggregates are formed after landing of the ablated material on the substrate surface by a diffusive mechanism. Finally we discuss the role of the thermal conductivity of the substrate and the laser fluence on the properties of the fractal nanostructures. Our results represent an advancement towards controlling the production of fractal nanostructures by pulsed laser deposition., Comment: 21 pages

Many-body interactions with the underlying bulk electrons determine the properties of confined electronic states at the surface of a metal. Using momentum resolved nonlinear photoelectron spectroscopy we show that one can tailor these many-body interactions in graphite, leading to a strong renormalization of the dispersion and linewidth of the image potential state. These observations are interpreted in terms of a basic self-energy model, and may be considered as exemplary for optically induced many-body interactions.

The crystallization behavior of two new stable glasses belonging to the BaO−K2O−Na2O−Nb2O5−SiO2 system, synthesized by the melt-quenching technique, was studied with the aim to obtain nanostructured glasses based on tungsten−bronze phases. Nanostructured samples with valuable second harmonic generation (SHG) activity were obtained starting from 8BaO·15Na2O·27Nb2O5·50SiO2 glass after suitable heat treatments performed in the glass transition range, by means of the bulk nucleation mechanism. The influence of the devitrification mechanism on the SHG efficiency was clarified with particular reference to the effect of structural modifications on the transparency of the nanostructured glasses. These samples are formed by Ba2NaNb5O15 nanocrystals (about 15 nm in size) randomly dispersed in a phase-separated amorphous matrix. Their SHG efficiency is partially impaired by the Rayleigh scattering originated by the nanocrystals. These nanostructured glasses can be useful when the generation efficiency is not an issue, as in the diagnostics for ultrafast lasers, due to the independence of the second harmonic generation from the polarization state of the laser light and no need for preferential material orientation.

Unveiling the nature of the bosonic excitations that mediate the formation of Cooper pairs is a key issue for understanding unconventional superconductivity. A fundamen- tal step toward this goal would be to identify the relative weight of the electronic and phononic contributions to the overall frequency (\Omega) dependent bosonic function, \Pi(\Omega). We perform optical spectroscopy on Bi2212 crystals with simultaneous time- and frequency-resolution; this technique allows us to disentangle the electronic and phononic contributions by their different temporal evolution. The strength of the interaction ({\lambda}~1.1) with the electronic excitations and their spectral distribution fully account for the high critical temperature of the superconducting phase transition., Comment: 9 pages, 4 figures

Accelerated production of dry fermented sausages by shortening the drying-ripening process represents one of the new developments in meat product technology and is expected to have a promising future. However, food safety concerns, which could exist when processes are shortened, must be investigated in particular. In the present challenge test, the fate of Listeria monocytogenes and Salmonella was investigated in acid (pH 4.8) and low-acid (pH 5.3) chorizo that were fermented, thermally treated and dried either by the accelerated drying system QDS process® or the traditional process. Even though the innovative QDS process® substantially shortened the drying time when compared to the traditional drying system, results showed that in case of low level contamination of raw meat, the same product safety was achieved.

Using time-resolved reflectivity measurements on unaligned and aligned bundled single-wall carbon nanotubes with a pump energy of 1.55 eV, quasi-resonant with the second Van Hoye singularity of semiconducting tubes, a positive sign of the transient reflectivity is detected in unaligned nanotubes. In contrast a negative sign is detected in aligned nanotubes. This discovery addresses a long-standing question showing that in unaligned nanotubes the stronger intertube interactions favor the formation of short-lived free charge carriers in semiconducting tubes. A detailed analysis of the transient reflectivity spectral response shows that the free carriers in the photo-excited state of semiconducting tubes move towards metallic tubes in about 400 fs. (C) 2011 Elsevier Ltd. All rights reserved.

The response of the torsional modes of a thermally excited cantilever across the jump-to-contact transition shows a modification of the oscillation amplitude, frequency, and damping. The measurement of these parameters is important because their analysis provides nanoscale information on the physical, chemical, and topographic properties of the sample. The tip-surface interaction potential is usually reconstructed by Fourier analysis of the cantilever oscillations around its equilibrium position. However, Fourier analysis can be correctly interpreted only in the case of stationary systems. The wavelet transform analysis overcomes these limitations, revealing the temporal evolution of the spectral content of a temporal trace. The one-dimensional time signal from the photodiode is converted into a two-dimensional time-frequency topography, which simultaneously exhibits the time and frequency behavior of the cantilever thermal fluctuations. In the present study, we show preliminary data obtained using wavelet transforms to analyze thermally excited torsional cantilever modes during jump-to-contact transition on a highly oriented pyrolitic graphite surface in air. [DOI: 10.1380/ejssnt.2011.228]

Transparent glasses having molar composition (23-x)K{sub 2}O.xNa{sub 2}O.27Nb{sub 2}O{sub 5}.50SiO{sub 2} (x=0, 5, 10, 15 and 23) have been synthesized by the melt-quenching technique and their devitrification behaviour has been investigated by DTA and XRD. Depending on the composition, the glasses showed a glass transition temperature in the range 660-680 deg. C and devitrified in several steps. XRD measurements showed that the replacement of K{sub 2}O by Na{sub 2}O strongly affects the crystallization behaviour. Particularly, in the glasses with only potassium or low sodium content the first devitrification step is related to the crystallization of an unidentified phase, while in the glass containing only sodium, NaNbO{sub 3} crystallizes. For an intermediate sodium content (x=10 and 15) a potassium sodium niobate crystalline phase, belonging to the tungsten-bronze family, is formed by bulk nucleation. This system looks promising to produce active nanostructured glasses as the tungsten-bronze type crystals have ferroelectric, electro-optical and non-linear optical properties. Preliminary measurements evidenced SHG activity in the crystallized glasses containing this phase. - Graphical abstract: Synthesis of glasses (23-x)K{sub 2}O.xNa{sub 2}O.27Nb{sub 2}O{sub 5}.50SiO{sub 2} (x=0, 5, 10, 15 and 23) from which SHG active phases crystallize by bulk nucleation for non-linear optical nanostructured glasses.

The way organic thin films properties are affected by molecular interactions at surfaces is an important research topic because thin molecular films constitute a model system for biological research and have applications ranging from light-emitting diodes and solar cells to chemical sensors. In this work, the formation of thin films of Methylene Blue in aqueous solution at a fused quartz surface was investigated with evanescent wave absorption spectroscopy, using a continuum spectrum generated in a non-linear fiber by short laser pulses.

The use of femtosecond laser pulses to impulsively excite thermal and mechanical transients in matter has led, in the last years, to the development of picosecond acoustics. Recently, the pump-probe approach has been applied to nano-engineered materials to optically generate and detect acoustic waves in the GHz-THz frequency range. In this paper, we review the latest advances on ultrafast generation and detection of thermal gradients and pseudo-surface acoustic waves in two-dimensional lattices of metallic nanostructures. Comparing the experimental findings to the numeric analysis of the full thermo-mechanical problem, these materials emerge as model systems to investigate both the mechanical and thermal energy transfer at the nanoscale. The sensitivity of the technique to the nanostructures mass and shape variations, coupled to the phononic crystal properties of the lattices opens the way to a variety of applications ranging from hypersonic waveguiding to mass sensors with femtosecond time-resolution.ens the way to a variety of applications ranging from hypersonic waveguiding to mass sensors with femtosecond time-resolution., Comment: 20 pages, 6 figures. Published on IEEE Photonics Journal

In this review we describe the development of ultrafast non-linear photoemission spectroscopy on metals from the first historic observations in the sixties to state-of-the-art experiments. We present an account that is focused on electron spectroscopy experiments that use short laser pulses to investigate the non-equilibrium response of electrons in metals. Several examples of the application of non-linear spectroscopy to the investigation of many-body effects and highly non-equilibrium processes will be illustrated. Furthermore, we give a brief overview of the wide spectrum of experimental methods based on non-linear photoemission spectroscopy.

Fractal TiO2 nanostructures in crystalline form are obtained at ambient pressure and temperature by pulsed laser deposition with femtosecond pulses. The synthesized structures have been studied by scanning electron microscopy, Raman spectroscopy, and X-ray photoemission spectroscopy. We show that the dendritic aggregations deposited on silicon wafers at room temperature are fractals. They are composed by nanoparticles with an average diameter in a range below 20 nm, with the presence of larger nanoparticles with a diameter above 50 nm. We demonstrate that the fractal dimension and area can be tuned by varying laser fluence and sample/target distance. X-ray photoemission spectroscopy shows that the as-deposited nanostructures are TiO2 while Raman spectroscopy reveals that the crystalline structure of fractals and nanoparticles are composed either by rutile or anatase phase, with a dominant relative concentration of anatase. We discuss possible mechanism of fractals and nanoparticles formation in comparison with the literature results.

Ultrafast broadband transient reflectivity experiments are performed to study the interplay between the nonequilibrium dynamics of the pseudogap and the superconducting phases in Bi2Sr2Ca0.92Y0.08Cu2O8+δ. Once superconductivity is established, the relaxation of the pseudogap proceeds ∼2 times faster than in the normal state, and the corresponding transient reflectivity variation changes sign after ∼0.5 ps. The results can be described by a set of coupled differential equations for the pseudogap and for the superconducting order parameter. The sign and strength of the coupling term suggest a remarkably weak competition between the two phases, allowing their coexistence.

The transient eigenmode structure of an interacting cantilever during a single impact on different surfaces evidences the excitation of higher flexural modes and low frequency oscillations. The frequency shift of the fundamental mode after the tip comes into contact with the sample surface allows calculating the tip–sample interaction stiffness and evidences the role of capillary condensation and surface wettability on the cantilever dynamics. Wavelet transforms are used to trace the origin of spectral features in the cantilever spectra and calculate force gradients of the tip–sample interaction.

International audience; The impulsive acoustic dynamics of soft polymeric surface phononic crystals is investigated here in the hypersonic frequency range by near-IR time-resolved optical diffraction. The acoustic response is analysed by means of wavelet spectral methods and finite element modeling. An unprecedented class of acoustic modes propagating within the polymer surface phononic crystal and confined within 100 nm of the nano-patterned interface is revealed. The present finding opens the path to an alternative paradigm for characterizing the mechanical properties of soft polymers at interfaces and for sensing schemes exploiting polymers as embedding materials.

An optical discrimination technique, tailored to nanometric-sized, low optical absorbance molecular complexes adhering to thin metal films, is proposed and demonstrated. It is based on a time-resolved evanescent-wave detection scheme in conjunction with hierarchical cluster analysis and principal value decomposition. The present approach aims to differentiate among molecular films based on statistical methods, without using previous detailed knowledge of the physical mechanisms responsible for the detected signal. The technique is open to integration in lab-on-a-chip architectures and nanoscopy platforms for applications ranging from medical screening to material diagnostics.