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International audience; The crystal structure of p-synephrine was solved from a high-resolution X-ray powder diffraction pattern optimized by energy-minimization calculations using the Dreiding force field. The title compound crystallizes in a monoclinic system (space group P2 1 /c, Z = 4, with a = 8.8504(11) Å, b = 12.1166(15) Å, c = 9.7820(11) Å, ␤ = 122.551(2) • , V = 884.21(19) Å 3 and d = 1.256 g cm −3). Since p-synephrine degrades upon melting, its melting data were determined from DSC experiments carried out as a function of the heating rate. This method allowed determining a melting temperature and enthalpy equal to 199.8 ± 1.3 • C and 57 ± 3 kJ mol −1 , respectively.

Polyethylene, cellulose and their blends with different compositions (5–30% cellulose content) were exposed to UV radiation or composted in soil for bio-degradation. Both types of degradation were carried out under laboratory conditions (room temperature, air atmosphere). The course of degradation processes has been studied using ATR-FTIR and Raman spectroscopies. There are practically no changes in spectra of photo- or bio-degraded pure PE films and cellulose powders. In contrast, the PE/cellulose blends are less stable than pure components and the processes of photodegradation seem to depend on blend composition and irradiation time. Prolonged UV exposure (100 h) leads to efficient photo-oxidation of blends studied. Biodegradation effect was also pronounced in PE films containing 30% cellulose.

We determine the phase diagram of the ferromagnetic (F)/superconducting (S) atomic superlattice with arbitrary coupling between the layers. The exchange field acting on F layers may induce different kinds of modulated superconducting phases with either in-plane modulation or a phase shift between adjacent S layers. When the exchange field is increased, the re-entrance of the superconductivity emerges and the "π phase" where the superconducting order parameter changes its sign in successive S layers is realized.

The recent extension of time-resolved femtosecond optical techniques to the investigation of the ultrafast electron scattering processes in metal clusters offers the unique possibility to follow their evolution from a bulk to a confined metal. The size dependent results obtained in model materials, the noble metals, are presented, focusing on the impact of the confinement on energy redistribution processes (electron–electron and electron–phonon coupling). Their application to the investigation of the acoustic vibration property of cluster and to the cluster-surrounding matrix energy transfers are also discussed. To cite this article: N. Del Fatti, F. Vallee, C. R. Physique 3 (2002) 365–380.

In conducting two-dimensional laminar and turbulence experiments, use of a vertical flowing soap film is often a good choice. However, one of the most frequently encountered and yet highly nontrivial problems is to measure the thickness of the film precisely. We propose a solution to this problem based on the strong absorbtion of infrared light by the water molecules in the film. At λ≃3 μm, a thin sheet of water is essentially opaque. The extinction length of 0.9 μm serves as a precise ruler for gauging the film thickness. Although only the time-averaged, single-point measurements are presented, the technique is general and can be used for multipoint measurements to investigate turbulent driven spatiotemporal fluctuations of the film thickness.

We report a shear-induced sponge (L3) to lamellar (L(alpha)) transition in a surfactant system. Under a constant shear rate, after a delay time t(n) we observe random nucleation and subsequent growth of the L(alpha) phase, demonstrating that the shear-induced transition is first order. A simple argument for the energy of a two-dimensional nucleus accounts for the observed delay and its shear-rate dependence.

We present a frequency-domain phase measurement technique coupled with a numerical chirp processing of the recorded sonogram to realise a pulse characterisation. Applications to the propagation of ultrashort pulses in linear and nonlinear media are investigated. Calibration of the experimental setup is performed using spectral interferometry technique. Results on linear dispersion glass and Kerr effect in vitreous samples are presented.

In this work, we study borate glasses doped with a low concentration of iron oxide by X band (9.5 GHz) electron magnetic resonance. These glasses (composition: 0.63B2O3–0.37Li2O–0.75×10−3 Fe2O3 in mole %) were annealed at increasing temperatures Ta, starting at the glass transition temperature. A new composite resonance at gef≈2.0 arises in the spectra measured at room temperature (300 K). The narrow component of this resonance is predominant in glasses annealed at lower Ta while the broad component increases in intensity as Ta increases. This resonance is ascribed to an assembly of superparamagnetic nanoparticles of a crystalline iron-containing compound. Numerical simulations assuming a lognormal particle volume distribution show that the mean particle diameter increases from 5.3 to 8.5 nm as Ta increases from 748 to 823 K. The integrated spectra intensity shows that the total number of spins in the nanoparticles increases rapidly with Ta. At lower anneal temperatures Ta, a striking increase occurs in t...

Time-resolved shadow imaging and novel two-color interferometric imaging have been developed for the investigation of optical breakdown induced in water by 100 fs laser pulses with a spatial resolution better than 5 μm. With a femtosecond time resolution, we clearly identified induced-plasma and filamentation formations, as well as the shock-wave expansion. Using the two-color interferometric imaging technique together with a conventional Mach–Zehnder interferometer, we investigated the phase shift of the interference fringes produced in water by the femtosecond optical breakdown. For different pump energies, at 40 ns after the breakdown, we estimated the water temperature to be between 30°C and 60°C and the water pressure between 10 and 40 MPa at the shock-wave front.

We present a lattice model based on two n→0 spin vectors, capable of treating the thermodynamics of living networks in micellar solutions at any surfactant concentration. We establish an isomorphism between the coupling constants in the two spin vector Hamiltonian and the surfactant energies involved in the micellar situation. Solving this Hamiltonian in the mean-field approximation allows one to calculate osmotic pressure, aggregation number, free end and cross-link densities at any surfactant concentration. We derive a phase diagram, including changes in topology such as the transition between spheres and rods and between saturated and unsaturated networks. A phase separation can be found between a saturated network and a dilute solution composed of long flexible micelles or a saturated network and a solution of spherical micelles.

Observation of the very early stage of phase separation is made difficult by the large number of nucleated domains and the polydispersity of the droplet distribution. We investigate this issue using laser waves to locally quench a liquid mixture with two intersecting pump beams whose interference pattern traps the nuclei on the fringes. The time-resolved reflectivity of a third probe wave on the induced droplet grating (i) confirms that nucleation is heterogeneous even in the bulk, and (ii) surprisingly shows that impurities lead to an unexpected reduction of the growth onto a single ``medium-dependent master curve'' when samples are synthesized with the same lots of constituents.

Due to the weakness of the fluorescence signal from a single fluorophore, a scanning near-field optical microscope for single molecule spectroscopy requires a very efficient setup for the collection and detection of emitted photons. We have developed a home-built microscope for operation in a l-He cryostat which uses a solid parabolic mirror in order to optimize the fluorescence collection efficiency. This microscope works with Al-coated, tapered optical fibers in illumination mode. The tip-sample separation is probed by an optical shear-force detection. First results demonstrate the capability of the microscope to image single molecules and achieve a topographical resolution of a few nanometers vertically and better than 50 nm laterally.

We study the rheological properties of self-assembled surfactant structures: lyotropic liquid crystals exhibiting plane lamellar and ‘‘onion’’ ~concentric bilayer! textures. Both systems behave similarly: they are gel-like and exhibit extreme shear-thinning behavior. We demonstrate that this results in a hysteresis in the stress-strain curve when the stress is imposed. Controlled shear-rate experiments reveal the origin of the hysteresis by demonstrating the existence of two extrema in the stress-strain curve. The bistability leads to the formation of shear bands in the system and is illustrated by demonstrating the existence of sudden jumps in the viscosity of the fluid, following the viscosity of the fluid in time. @S1063-651X~98!01208-2#

Photosensitive textured WS2 and MoS2 films can be obtained by the techniques of reactive sputtering and solid state reaction, as long as the substrates used are each coated with a 10–20 nm Ni layer. When MS2 (M = W, Mo) layers are deposited onto these substrates and then annealed for half an hour at 1073k in an argon atmosphere, textured films crystallized in the 2H-MS2 structure are obtained, with their c crystallite axes perpendicular to the plane of the substrate. The films are nearly stoichiometric. The crystallinity enhancement of the films can be attributed to an improvement in the crystallization process related to liquid NiS phases present at the grain boundaries during annealing. Residual phases (NixSy; Ni;…) are distributed at the grain boundaries and do not strongly disturb the properties of the WS2 and MoS2 films. The optical absorption spectra are similar to those of single crystals, and the high photosensitivity of the films is attributed to a grain size enhancement by the NiS phase.

We report a new application of Forward Degenerate Four Wave Mixing to the two-photon transition 2p → 3p of atomic oxygen. This spectroscopy has been used to detect oxygen atoms produced in a microwave discharge. The possibility to determine number densities over a range of microwave plasma parameters is investigated. In contrast to conventional linear techniques, quantitative data are relatively easy to obtain even for environments with high background luminosity, limited optical access and inhomogeneous quenching.

We discuss the static and dynamic critical behavior of binary solutions of water with some alkyl-oxyethylene-glycol monoether (CiEj) and of di 2 ethylhexyl sodium sulfosuccinate (AOT)-water-decane ternary microemulsion systems. Extensive sets of measurements of the scattered light intensity, of the order-parameter fluctuations time correlation function, and of the shear viscosity, have been performed for different systems. In most of the cases our data sets show systematic deviations from the behavior usually observed for molecular binary fluids. We show that generalized hydrodynamics cannot account for these deviations. A modified version of the Sorensen et al. (1976) dynamical droplet model has been worked out. This model which assumes that the physical clusters formed close to the critical point can be treated like percolating aggregates, and which includes the finite size of the monomers, very well accounts for all our experimental results.

Impurities found in polyethylene and n-hexadecane give rise to intense and narrow single molecule lines at liquid helium temperatures. The fluorescence spectra of several impurity molecules in both matrices are nearly identical, suggesting that a single well-defined compound is involved. This paper summarizes all the photo-physical properties that may help identify the chemical structure of these impurities.

A monochromatic millimeter wave system coupled with an infrared temperature sensor has been used to investigate pictorial artworks. The flexibility of the system makes it possible to rapidly reveal buried layer information such as a graphite handmade sketch covered by paintings.

Flexible monochromatic millimeter wave system coupled with an infrared temperature sensor demonstrates large size 3D visualization of manufactured opaque phantoms with different refractive index contrasts. Peculiarities such as boundary effects, refraction and diffraction losses will be discussed.

An original double side photolithography method on ultrathin polymer and a laser micromachining technique were used to fabricate different fishnet structures. We performed simulations and experiments by terahertz time domain spectroscopy (THz-TDS from 100GHz to 3THz) respectively. The effective parameters were extracted with a single shot approach.

International audience; We demonstrate experimentally that a one-dimensional photonic crystal with a homeotropic nematic liquid crystal defect behaves as a polarization-sensitive nonlinear all-optical device. We study statics and dynamics of the nonlinear optical response for linearly and circularly polarized beams and show enhanced light sensitivity and polarization self-modulation effects

We evidenced the polarization rotation in an Yb^{3+} rod type fiber amplifier injected by a subnanosecond microlaser. Simple numerical simulations account for the observed phenomena.

We report on metamaterials which exhibit a tunable interval of negative effective permeability within 0.2–0.36 THz. They consist of a strontium titanate platelet, which shows a high and temperature tunable permittivity, with an array of laser engraved slits. The negative permeability then is due to a resonant confinement of the electromagnetic field within the rods. The range of negative permeability is determined by the geometry and the permittivity of the material used.

A Q-switched laser system which couples two ytterbium doped fibers is presented. Depending on the pump intensity this system yields either short or long nanosecond pulses. The gain competition accounts for the observed phenomena.

International audience; Three conditions for non-collinear third harmonic generation by a PTR glass volume Bragg grating are demonstrated using infrared ultrashort pulse illumination. Each condition corresponds to a different angle of grating orientation and a separate generation mechanism. We identify the mechanisms as corresponding to sum-frequency generation, Bragg diffraction of 3 omega, and a non-resonant Bragg condition involving three. photons interacting with a nonlinear grating vector. Theoretical modeling is performed using wave vector additions and the results are compared to experimental measurements

Solutions of the synthetic clay Laponite are strongly viscoelastic, even at very low particle concentrations. The formation of a gel, evidenced by the existence of a fractal network, has been invok...

We demonstrated a room-temperature detection of terahertz radiation with a plasma wave nanometric transistor. The detection is resonant and can be efficient for terahertz time-resolved imaging.

Gold nanoparticles are now widely used in different fields of chemistry, physics and biology. For many applications, it became crucial to use the smallest ones and at the same time to be able to detect them at the single particle level with versatile optical methods. Such methods should also allow the study of their intimate optical properties. Here we review the ultra-sensitive optical methods based on the photothermal effect which permit the detection of individual gold nanoparticles down to 1.4 nm through their absorption. The absorption spectroscopy of the Surface Plasmon Resonance of individual gold nanoparticles down to 5nm is further presented and revealed intrinsic size effects in the optical response of the smallest nanoparticles. Different applications to biology are also presented such as for new types of gold nanoparticles based DNA microarrays and for live cell molecular imaging owing to the insensitivity of the photothermal methods to scattering environments.

The electronic and nuclear contributions to nonlinear optical properties of niobium oxide-based glasses have been measured using third-harmonic generation and pump-probe techniques. The results have been found to be in agreement with Hellwarth's model for niobium oxide $({\mathrm{Nb}}_{2}{\mathrm{O}}_{5})$ concentrations below $30\phantom{\rule{0.3em}{0ex}}\mathrm{mol}\phantom{\rule{0.2em}{0ex}}%$. Above $30\phantom{\rule{0.3em}{0ex}}\mathrm{mol}\phantom{\rule{0.2em}{0ex}}%$ ${\mathrm{Nb}}_{2}{\mathrm{O}}_{5}$, discrepancies with the theoretical model have been observed. It has been found that high niobium ion content induces a change of the local structure within the glass and favors the formation of three-dimensional blocks of corner-sharing ${\mathrm{NbO}}_{6}$ octahedra. Since similarities with crystalline structures are present, we propose that some specific collective vibrational modes could be at the origin of the extra nuclear contributions to the optical Kerr effect.

(2005). Thermal Protection Using Molecular Alloys As Phase Change Materials. Materials Research Innovations: Vol. 9, No. 3, pp. 76-77.

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In the context of a general investigation of the nonlinear optical properties of glasses, we report here the effect of introducing TiO 2 in various silicate and borophosphate glass matrixes. A correlation study is carried out between the magnitude of the measured nonlinear indices n 2 of these materials and the local structure around titanium which can be deduced using XAFS analysis. This allows to point out that square-based pyramids are particularly efficient when present in borophosphate glasses.

In this paper, we present a simple way to increase the sensitivity of polarization modulation infrared reflection-absorption spectroscopy (PM-IRRAS) for the study of ultrathin films deposited on dielectric and semiconductor substrates. The enhancement of the absorption band intensity is obtained by reducing the signal arising from the substrate. This is achieved by adding a polarizer after the sample in order to balance the polarized reflectivities of the sample. As a consequence, the contribution of the film to the PM-IRRAS signal is increased relative to that of the substrate. An enhancement factor of about 10 has been obtained for ultrathin organic films deposited on glass and spread at the air-water interface. This method has also allowed the study of the very thin native oxide layer present on silicon without the need for the reference spectrum of bare silicon.

In this paper, we report about an application of the two-color laser-induced thermal gratings technique in the visible region to the detection of nitrogen dioxide in mixtures of nitrogen and argon at total pressure ranging up to 1 bar. We have investigated the dependence of the signal on the gas mixture parameters (pressure, NO 2 concentration, collision partners) and on the laser properties (beams polarization, pulse energy, bandwidth) at various instants during the temporal evolution of the thermal grating. Comparison of experimental results and theoretical predictions is performed. Finally, the detectivity of 4 ppm was obtained at normal conditions of pressure (1 bar) and temperature (300 K).

In this paper, we present some preliminary results on a new terahertz-Time Domain Spectroscopy (THz-TDS) experiment. After a general introduction about the interest of the THz range, we particularly discuss some advantages of this technique for combustion applications and compare it with the classical linear and nonlinear optical techniques. The set-up developed in our laboratory is described and some results on NO displayed.

In this paper, a dynamical force microscopy study of self-assembled monolayers of organosilanes, grafted onto a silica support, is reported. Organosilanes, terminated either with a functional group (ethylene glycol) or with a methyl group, were used. The influence of the reaction time and the solvent composition on the grafting was investigated to improve the homogeneity of the self-assembled monolayers. Numerical simulations of approach−retract curves, obtained in the tapping mode, were performed and compared to experimental ones. Information such as mechanical response and height of the grafted organic layers has been obtained.

We study a simple model for an amphiphilic layer that may adsorb cosurfactant molecules from a reservoir. Upon varying the length of the cosurfactant, we obtain a discontinuous change of the adsorption rate and a corresponding discontinuity of the bending rigidity kappa. With realistic values for the chemical potential and the interaction energy of the hydrophobic tails, our model accounts quantitatively for the measured rigidity and the discontinuity observed for the ternary system AOT/water/oil and for SDS/alcohol bilayers.

Application of time-resolved femtosecond spectroscopy to the investigation of the ultrafast electron kinetics in metallic materials is reviewed. The main experimental techniques are presented and the results obtained on electron scattering processes discussed in bulk metals and nanoparticles, focusing on the energy redistribution processes (electron–electron and electron–phonon coupling) and electronic transport. Application of the femtosecond techniques to the investigation of the acoustic vibrations of metal films and nanoparticles is also presented.

We describe a new type of low-cost easy-to-use viscometer based on the temperature elevation in a liquid under shear flow. After calibration, this instrument can be used to measure the apparent steady state viscosity for both Newtonian and non-Newtonian liquids with no yield stress. We compute the rise in temperature due to viscous dissipation in a Couette cell and compare it to experimental results for different fluids. We show that the variation of the temperature with shear rate can be used to characterize the rheological behaviour of viscous fluids and to evaluate their viscosity in a large domain, from typically a few cP up to more than 10 P, with an accuracy of about ±5%. In contrast to simple viscometers, non-Newtonian fluids can be studied with this apparatus. We give experimental results for Newtonian and non-Newtonian liquids and show that they are very similar to those given in the literature by using much more sophisticated instruments.

Dynamic light scattering experiments on lyotropic lamellar phases of brine and surfactant subjected to a flow field have been realized. The obtained results reveal that the relaxation times measured depend strongly on the velocity of the flow. This dependence is indicative of an increase of the effective elasticity modulus K and a decrease of the effective compressibility modulus (-)B of the lamellar phase with the flow velocity. This leads to the conclusion that the shear can induce a suppression of the undulation fluctuations of the bilayers of the lamellar phase. Our results show also that the rigidity of the membranes decreases as the salt concentration of the sample increases.

We report conductivity measurements on solutions of closed compact monodisperse multilamellar vesicles (the so-called "onion texture") formed by shearing an inverse lyotropic lamellar L(alpha) phase. The conductivity measured in different directions as a function of the applied shear rate reveals a small anisotropy of the onion structure due to the existence of free oriented membranes. The results are analyzed in terms of a simple model that allows one to deduce the conductivity tensor of the L(alpha) phase itself and the proportion of free oriented membranes. The variation of these two parameters is measured along a dilution line and discussed. The high value of the conductivity perpendicular to the layers with respect to that of solvent suggests the existence of a mechanism of ionic transport through the insulating solvent.

We report the effect of shear flow on a phase-separated system composed of lyotropic lamellar (L(alpha)) and sponge (L3) phases in a mixture of brine, surfactant, and cosurfactant. Optical microscopy, small-angle light, and x-ray scattering measurements are consistent with the existence of a steady state made of multilamellar ribbon-like structures aligned in the flow direction. At high shear rates, these ribbon-like structures become unstable and break up into monodisperse droplets resulting in a shear-thickening transition.

We theoretically describe and experimentally explore the kinetics of holographic grating formation resulting from different laser-induced phase separation mechanisms. Our method makes use of two interfering c.w. laser waves to quench binary mixtures in composition, and to optically trap the nucleated domains on the fringes. Essentially, two different processes can lead to these variations in concentration: electrostriction and thermodiffusion. The former originates from induced dipolar couplings in a field gradient; as photopolymerization, this is a local process which is essentially sensitive to the ${q=q}_{0}$ Fourier mode forced by the fringe modulation. The latter corresponds to a variation in composition driven by a small thermal gradient; as solvent evaporation and thermal heating techniques, it is nonlocal and behaves as ${1/q}^{2}$ because of its dissipative origin. By making experiments in both cases, we show that this q dependence on excitation has a strong influence on the performance of holographic gratings. While in the first case reflectivity saturates because the phase transition is confined by the fringes which behave as separated optical boxes with ``soft walls'' which calibrate the droplet size, blurring is expected for fringe-trapped domains induced by a nonlocal phase transition because the transition is governed by the Gaussian shape of the pump beams, and nucleated domains can reach a much larger size than the fringe spacing. The good agreement observed with our general model clearly illustrates how to make the difference between local and nonlocal excitations, and offers a first step towards a unified description of holographic grating formation monitored by phase transitions.

We study the tail contributions to the elastic constants of an amphiphilic layer. For dense systems the terms arising from the attractive van der Waals interactions prevail, whereas the translational entropy of the liquid layer is essential at lower density. Both the membrane rigidity kappa and the Gaussian bending elastic constant kappa; strongly vary with the density of the hydrocarbon chains; for dense systems, they are of the order 100kT with a ratio kappa;/kappa = -2 / 3. At lower density, partial cancellation of interaction and entropic contributions leads to elastic constants of the order of kT, with a ratio close to the value -2 observed for microemulsions.

We have designed a simple mid-IR femtosecond OPA seeded by a white-light continuum and delivering very stable, largely tunable and energetic output pulses. This OPA requires fewer than 200 μJ of 120-fs Ti:sapphire pump pulses as energy. This system allowed us to experimentally compare the performances of potassium crystals (KTP, KTA, and KNbO3) for the generation of up to 100-fs Fourier-transform-limited pulses tunable in 1–4.6 μm mid-IR wavelengths.

The flow-structure relation of lamellar phases is studied using rheometry and cross-polarized microscopy under flow. The equilibrium phases show different defects. Low salinities lead to very viscous, "onion" phases, whereas at high salinity, a low viscosity plane lamellar phase is found. Under shear, the latter shows a sudden transition to a viscoelastic gel, with a texture and viscosity very similar to that of the onions. Gelation occurs after a certain delay time, increasing rapidly with salinity, by the nucleation of onions. This allows one to relate the delay time to the defect energy.

We show the existence under shear flow of steady states in a two-phase region of a brine-surfactant system in which lyotropic dilute lamellar (non-Newtonian) and sponge (Newtonian) phases are coexisting. At high shear rates and low sponge phase-volume fractions, we report on the existence of a dynamic transition corresponding to the formation of a colloidal crystal of multilamellar vesicles (or "onions") immersed in the sponge matrix. As the sponge phase-volume fraction increases, this transition exhibits a hysteresis loop leading to a structural bistability of the two-phase flow. Contrary to single phase lamellar systems where it is always 100%, the onion volume fraction can be monitored continuously from 0 to 100 %.

Noncollinear frequency conversion of two femtosecond pulses is used to characterize the nonlinear profile induced in thermally poled fused silica. This technique permits one to deduce the nonlinear profile and the charge distribution induced by the poling treatment. These data and the current that passes through the sample during the poling are consistent with the occurrence of a built-in electric field associated with the diffusion of two ionic species.

International audience; no abstract