Search

International audience; Lasers and amplifiers based on thulium-doped silica fibers require improved spectroscopic properties. In this context, one of the most promising approaches is based on the embedding of thulium ions in nanoparticles of tailored composition and structure. This paper presents various methods used to produce thulium-doped nanoparticles inside silica-based optical fibers. Effects of solution doping method during the elaboration of Modified Chemical Vapor Deposition preform and doping solution composition are studied. A comparison is made between the use of solutions containing LaF3:Tm3+ or YAG:Tm3+ nanoparticles and aluminum-lanthanum-thulium chlorides. Results show that for similar lanthanum content, lanthanum-thulium chlorides doping allows for similar enhancement of H-3(4) level of Tm3+ than LaF3:Tm3+ doping. Also, effects of aluminum on H-3(4) lifetime enhancement and inhibition of nanoparticle's formation is discussed.

International audience; We review several propagation models that do not rely on the slowly-varying-envelope approximation (SVEA), and can thus be considered as fundamental models addressing the formation and propagation of few-cycle pulsed field structures and solitary waves arising in the course of intense ultrashort optical pulse evolution in nonlinear media and beyond octave-bandwidth optical spectrum broadening. These generic models are: the modified-Korteweg-de Vries (mKdV), the sine-Gordon (sG), and the mixed mKdV-sG equations. To include wave polarization dynamics, the vector extensions of both mKdV and sG equations are introduced. Multi-octave-spanning supercontinuum generation and few-cycle soliton structures are highlighted from numerical simulations.

This chapter gives a comprehensive review of collective soliton dynamics in passively mode-locked fiber lasers. It is first presented the multiple-pulsing properties occurring in ultrashort pulse fiber lasers. Theoretical and experimental results emphasize on multistability and hysteresis phenomena. Then we consider the formation of bound states obtained with high pumping power and involving hundreds of identical solitons, especially when the soliton distribution is analogous to the periodic arrangement of atoms in a crystal. The recent interest for complex multisoliton dynamics is covered. The soliton rain dynamics, which displays some analogy with the water cycle, is presented. Dynamics analogous to various states of matter, and chaotic multiple pulse dynamics, including noise-like pulses and dissipative rogue waves are also reported. It is evidenced that all these complex soliton patterns, which do not depend on the exact mode-locking mechanism, possess some universal character. We finally provide recent experimental developments of harmonic mode-locked (HML) fiber lasers, pointing out the possibility to induce HML by an external continuous component.

International audience; Bulk glasses having the compositions As 42 S 58 , As 36 Sb 6 S 58 , and As 36 Ge 6 S 58 have been irradiated at 800 nm using a femtosecond-pulsed laser to determine the relationship between composition and photo-response. Localized variation in the glass volume (photo-expansion) has been determined through interferometric measurements of surface exposures, whereas induced refractive index change (photo-darkening) was determined from the diffraction efficiency of subsurface direct-written phase gratings. To understand the compositional dependence of the photo-response, the linear and nonlinear optical properties and structure of the unexposed glasses have been compared. The ablation threshold is shown to be controlled by variation of the nonlinear absorption, related to shifts of the absorption band gap with exchange of As by Ge or Sb. Changes in the unexposed network structure show that partial replacement of As by Ge or Sb induces an increased number of As–As bonding defects in the glass, particularly in the form of As 4 S 4 molecular units which become polymerized into the network, impacting the photo-modification process. The Ge was found to induce an increase in the ablation threshold, and enhance both photo-darkening and photo-expansion effects, whereas Sb was shown to decrease ablation threshold and inhibit photo-darkening while enhancing photo-expansion.

International audience

International audience; A general study of the diffracted far field due to thermal lens heating using Gaussian beams is presented. The numerical simulation considers the whole system, including both the optical and the thermal parameters. It is shown that the existing simplified relations found in the literature and used up to now only give the order of magnitude of the thermo-optical coefficients. More accurate, simplified formulas are derived to measure the induced thermal phase shift when working with Z-scan-based methods. Temperature estimation in absorbing media turn out to be more reliable whether using time-resolved or steady-state techniques. The extension of the calculation to the image formation in a 4f system is also addressed.

Functionalized photochromic materials have attracted a growing interest during the last few decades since they are promising materials to be used in optoelectronics and photonics. In this paper, the results of the nonlinear optical (NLO) investigation (second and third harmonic generation) of spin deposited high-quality thin films of styrylquinoline containing methacrylic polymers studied by using Maker fringes technique employing 30 ps laser pulses at fundamental wavelength of 1064 nm are presented. Photochromic styrylquinoline units were oriented in the thin films by corona poling technique promoting second order NLO activity. Strong dependence of the NLO response upon the structure of the polymers has been found, which is related to the different charge transfer within the styrylquinoline fragments. These investigations were completed by theoretical studies using HOMO-LUMO energy levels theory and the first and second order hyperpolarizability values. Good compatibility has been achieved between the theoretical and experimental results. Studied styrylquinoline-based polymers showed the contrast in NLO response after their trans-cis photoisomerization making them interesting for using in photonic devices.

This editorial reports on a thorough analysis of the abundance and scarcity distribution of chemical elements and the minerals they form in the Earth, Sun, and Universe in connection with their number of neutrons and binding energy per nucleon. On one hand, understanding the elements’ formation and their specific properties related to their electronic and nucleonic structure may lead to understanding whether future solutions to replace certain elements or materials for specific technical applications are realistic. On the other hand, finding solutions to the critical availability of some of these elements is an urgent need. Even the analysis of the availability of scarce minerals from European Union sources leads to the suggestion that a wide-ranging approach is essential. These two fundamental assumptions represent also the logical approach that led the European Commission to ask for a multi-disciplinary effort from the scientific community to tackle the challenge of Critical Raw Materials. This editorial is also the story of one of the first fulcrum around which a wide network of material scientists gathered thanks to the support of the funding organization for research and innovation networks, COST (European Cooperation in Science and Technology). info:eu-repo/semantics/publishedVersion

International audience; Europium (Eu)-doped silica nanoparticles have attracted great interest for different applications, in particular in biomedicine as biosensors or for tissue regeneration. Sol-gel is the most common process used to prepare those particles, with size varying from tens to hundreds of nanometers. In this article, we focus our attention on the comparison between two commonly used sol-gel derived methods: reverse microemulsion (for particles smaller than 100 nm) and Stöber method (for particles larger than 100 nm). Europium concentration was varied between 0.2 and 1 mol%, and the nanoparticle diameters were 10, 50 and 100 nm. The link between the local environment of europium ions and their optical properties was investigated and discussed. Using Transmission Electron Microscopy, nitrogen sorption, X-ray diffraction, Fourier-Transform Infra-Red and pulsed doubled Nd:YAG laser, we confirmed that fluorescence lifetime was improved by thermal treatment at 900 °C due to the elimination of aqueous environment and modification of structure disorder. The size of nanoparticles, the amount of europium and the thermal treatment of obtained materials influence the emission spectra and the decay curves of Eu3+.

Third-order optical nonlinearity (TONL) of chalcogenide glasses (ChGs) in Ge-In-S (GIS) ternary system is characterized at two near-infrared wavelengths of 0.8 μm and 1.064 μm. It is found that the GIS ChGs with non-stoichiometric compositions exhibit extremely large TONL properties, and its origin has been explained from both aspects of glass structure and wavelength-dispersion dependence of the TONL properties. Nevertheless, calculation of figure of merits indicates that the GIS ChGs are suitable for n2-based TONL optical devices at long wavelength, while suitable for β-based devices at short wavelength.

The beam waist relative variation (BWRV) method known as a Z-scan based technique is used to demonstrate its feasibility in characterizing the thermal effects induced by a continuous laser beam in different materials. A study of several classical solvent-based solutions (water, ethanol, methanol …) is carried out before introducing the extension of the BWRV method to laterally map the tested sample. We show that the transverse xy-scan of the sample allows to extract an image of the phase shift due to local thermal heating. This new device, called XYZ-scan, is designed for the thermal characterization of inhomogeneous samples. An example will be given on an inhomogeneous 1.6 μ m thick thin film doped with silver nanoparticles.

We report the experimental study of triple-lobe wavelength double-clad co-doped Er:Yb fiber laser operating with a composite-state soliton regime. The passively mode-locked emission is achieved through nonlinear polarization rotation (NPR) technique. The three-lobe wavelengths oscillation, centred at 1567 nm, 1585 nm, and 1616 nm, is attributed to two phenomena; the nonlinear filtering based on intensity-dependent polarization rotation and the linear loss of the cavity impacting the population inversion (gain). Moreover, by fine adjustment of the polarization controllers, this complex regime still can be switched into harmonic states. This work shows a novel operation regime, which could help understanding the composite soliton dynamics in fiber lasers and could be useful for different applications in wavelength division multiplexed transmission systems and optical signal processing.

International audience; Developing new rare-earth-doped optical glasses with "enhanced" spectroscopic properties requires the elaboration of new glass compositions. To overcome some typical limitations of silica glass, a strategy consists in encapsulating rare-earth (RE) ions within oxide nanoparticles (NPs) through a phase separation mechanism. In this paper, Molecular Dynamics simulations were performed using an interatomic potential reproducing the phase separation within a MgO–SiO2 binary melt to obtain RE-codoped glass models with RE = Eu or Er. In these structures, we observed that Mg-rich regions, included into a silica-rich matrix and identified as NPs, are amorphous and exhibit a large range of sizes. We showed that such nanoparticles are the host of a depolymerization phenomenon of the NPs’ SiO4 tetrahedral network leading to a release of non-bridging oxygen atoms. In the NPs, the MgO concentration increases and the doping RE ions are mainly located into the NPs where they are over-concentrated compared with the nominal doping concentration. However, the induced clustering effect is limited because of the non-bridging-oxygen-rich environment encountered in the NPs. This numerical analysis allows to give an insight on the chemical composition of the NPs, and especially on the local environment of the encapsulated rare-earth ions.

International audience

We know that the modified Korteweg-de Vries (mKdV), the sine-Gordon (sG), and the mKdV-sG models can describe few-cycle optical pulse propagation beyond the slowly-varying-envelope approximation in transparent media. We show numerically that these models are also able to describe the generation of supercontinua with spectral bandwidths of several octaves. Several mechanisms of spectral broadening are highlighted, involving self-phase modulation, parametric interactions of high harmonics, and few-cycle-soliton generation.

International audience

We experimentally demonstrate spatial beam self-cleaning in an Yb-doped graded-index multimode fiber taper, both in passive and active configurations. The input laser beam at 1064 nm was injected for propagation from the small to the large core side of the taper, with laser diode pumping in a counterdirectional configuration. The Kerr effect permits to obtain high-beam quality amplification with no accompanying frequency conversions. As a result, our nonlinear taper amplifier may provide an important building block for multimode fiber lasers and amplifiers.

International audience; Ce livre s’adresse aux étudiants de master, aux jeunes doctorants et aux élèves ingénieurs s’intéressant de près ou de loin à l’optique et à la photonique. Il peut également constituer une source d’inspiration pour les enseignants-chercheurs.Y sont regroupés 23 problèmes avec des solutions détaillées, pour la plupart tirés de publications scientifiques récentes, offrant ainsi un panorama varié et actuel du domaine de l’optique non linéaire. Ces problèmes abordent des sujets aussi variés que les solitons spatiaux ou temporels, la génération d’harmonique dans un métamatériau ou bien l’absorption multiphotonique.Des compléments rappellent les notions de base en optique non linéaire et permettront d’aller plus loin dans la description des phénomènes.

This work is focused on the use of multilayer transparent conductive electrode (TCE) based on ZnO/Ag/ZnO in the fabrication of the organic heterostructures. The ZnO/Ag/ZnO obtained combining sputtering/thermal evaporation/sputtering techniques is featured by a good optical transmittance, a low electrical resistivity and a reduced roughness. All these characteristics recommend it as a viable alternative to indium tin oxide (ITO) for different applications. The organic materials, N,N'−diphenyl−N,N'−bis (1−naphthyl)−1,1´−biphenyl−4,4´−diamine (α-NPD), 5,12-Dihydro-5-12-dimethylquino [2,3-b]acridine-7,14dione (DMQA) and 4,7 diphenyl-1,10-phenanthroline (BPhen) were deposited by vacuum thermal evaporation (VTE) method, the properties of the obtained layers being investigated by FTIR, UV-VIS and PL) spectroscopy. The I-V characteristic (recorded in dark) of the organic heterostructure fabricated on the ZnO/Ag/ZnO electrode shows diode behavior, revealing its potential applications in the organic light emitting devices (OLED).

The nonlinear optical responses of Disperse Orange 3 (DO3) dissolved in tetrahydrofuran (THF) with different concentrations were investigated by Z-scan D4σ technique employing 12 ps and 17 ps pulses of Nd:YAG laser at 532 nm and 1064 nm, respectively. The comparison of the experimental results at both wavelengths demonstrates the strong influence of the resonant phenomena related to the linear absorption on the nonlinear response at 532 nm. In particular, DO3 solution was found to exhibit negative resonant nonlinear refraction with negligible saturable and multi-photon absorption. Moreover, the competition between negative and positive nonlinear refractive indices (n2) of the solute and the solvent was observed at low concentrations. The linear dependence of n2 on the latter quantity allowed to estimate an effective second-order hyperpolarizability of DO3 molecule at 532 nm.

Mixed layers of azomethine oligomers containing 2,5-diamino-3,4-dicyanothiophene as central unit and triphenylamine (LV5) or carbazol (LV4) at both ends as donor and fullerene derivative, [6,6]-phenyl-C61 butyric acid butyl ester ([C60]PCB-C4) as acceptor, have been prepared by Matrix Assisted Pulsed Laser Evaporation (MAPLE) on glass/ITO and Si substrates. The effect of weight ratio between donor and acceptor (1:1; 1:2) and solvent type (chloroform, dimethylsulphoxide) on the optical (UV–vis transmission/absorption, photoluminescence) and morphological properties of LV4 (LV5): [C60]PCB-C4 mixed layers has been evidenced. Dark and under illumination I–V characteristics of the heterostructures realized with these mixed layers sandwiched between ITO and Al electrodes have revealed a solar cell behavior for the heterostructures prepared with both LV4 and LV5 using chloroform as matrix solvent. The solar cell structure realized with oligomer LV5, glass/ITO/LV5: [C60]PCB-C4 (1:1) has shown the best parameters.

Organic heterostructures based on poly(3-hexylthiophene) (P3HT) and fullerene (C60) as blends or multilayer were deposited on Al:ZnO (AZO) by Matrix-Assisted Pulsed Laser Evaporation (MAPLE) technique. The AZO layers were obtained by Pulsed Laser Deposition (PLD) on glass substrate, the high quality of the films being reflected by the calculated figure of merit. The organic heterostructures were investigated from morphological, optical and electrical point of view by atomic force microscopy (AFM), UV–vis spectroscopy, photoluminescence (PL) and current-voltage (I–V) measurements, respectively. The increase of the C60 content in the blend heterostructure has as result a high roughness. Compared with the multilayer heterostructure, those based on blends present an improvement in the electrical properties. Under illumination, the highest current value was recorded for the heterostructure based on the blend with the higher C60 amount. The obtained results showed that MAPLE is a useful technique for the deposition of the organic heterostructures on AZO as transparent conductor electrode.

In this paper the influence of the heat treatment on the structural and optical properties of oxide single-layer and multilayer transparent thin film structures of ITO/Au/ITO, AZO/Au/AZO, TiO 2 /Au/TiO 2 and Bi 2 O 3 /Au/Bi 2 O 3 type is studied. The single-layer oxides and respective multilayer structures have been deposited on glass substrates by successive DC magnetron sputtering using metallic targets In:Sn, Zn:Al, Ti and Bi, in reactive (for the oxide films) or inert (for the metallic Au interlayer films) atmosphere. Good quality transparent conducting thin film structures have been obtained, with resistivity ∼10 −4 Ω cm and transmittance ∼75%. The wetting surface properties in function of time exposure at UV radiation (254 nm) have been also studied before and after heat treatment performed at 450 °C.

International audience; In this paper, we investigate experimentally the effect of an injected continuous external optical laser in a stable passive harmonic mode-locked fiber laser operating in the anomalous dispersion regime. Under specific conditions, the continuous-wave significantly increases the stability of the harmonic mode-locked regime. This occurs for a discrete set of wavelengths and below a critical injected power.

The herein thesis represents a complex study of photosensitive azopolysiloxanes and rejoins both theoretical and experimental techniques. The theme revolves around the azopolymer’s mass transport phenomenon induced by the photoisomerization of azobenzenes. Trans- to cis conversion of azobenzene and its derivatives is a reversible light actuated process that enables the rearrangement of surrounding matter at nano and micro level. This property is exploited to fabricate surface relief gratings (SRG) with certain geometrical features. The present studies are directed to comprehension of this complex mechanism, subject to great controversial among different research groups. The parameters that control the process are addressed and analyzed. Experimental study comprises the synthesis and characterization of four azopolysiloxanes which are then analyzed for the capacity to obtain SRG. Photochromic behaviour is evaluated through irradiation experiments at different light intensity, in the presence or absence of an assistance light that supposedly intensifies isomerization. Computer simulation focuses on diffusion of the molecules in the system: one azobenzene – like molecule (molecular motor) diluted in the host medium. Molecular modeling calculations are performed for motors with different lengths and with various isomerization times (fast or slow isomerization) in order to define the relation between these parameters and diffusion. Providing experimental and theoretical info on azopolymers is part of the SRG formation insight.; La présente thèse représente une étude complexe des azopolysiloxanes photosensibles et rejoint les techniques théoriques et expérimentales. Le thème tourne autour du phénomène de transport de masse des azopolymères induit par la photoisomérisation des azobenzènes. La conversion transt – cis de l'azobenzène et de ses dérivés est un processus réversible actionné par la lumière, qui permet le réarrangement de la matière environnante au niveau nano et micro. Cette propriété est exploitée pour fabriquer des réseaux de relief de surface (SRG) avec caractéristiques géométriques specifiques. Les présentes études visent à comprendre ce mécanisme complexe, sujet à une grande controverse parmi les différents groupes de recherche. Les paramètres qui contrôlent le processus sont traités et analysés. L'étude expérimentale comprend la synthèse et la caractérisation de quatre azopolysiloxanes qui sont ensuite analysés pour leur capacité d'obtenir des SRG. Le comportement photochromique est évalué par des expériments d'irradiation à différentes intensités lumineuses, en présence ou l'absence d'une lumière d'assistance qui devrait intensifier l'isomérisation. La simulation informatique se concentre sur la diffusion des molécules dans le système: une molécule de type azobenzène (moteur moléculaire) diluée dans le milieu hôte. Des calculs de modélisation moléculaire sont effectués pour des moteurs de différentes longueurs et avec différents temps d'isomérisation (isomérisation rapide ou lente) afin de définir la relation entre ces paramètres et la diffusion. Fournir des informations expérimentales et théoriques sur les azopolymères, est trop important pour comprendre la formation de SRG.

Rare-earth (RE) doped optical fibers are extensively used in lasers and optical amplifier devices. These key applications rely on the qualities of silica glass: mechanical and chemical stability, high optical damage threshold, low cost, etc. However, silica glass has certain characteristics which may make it less efficient compared to other types of glass, particularly in some potential applications using RE ions: high phonon energy, low solubility of RE ions, etc. To overcome these limitations, one recent strategy consists of developing a fabrication method which triggers RE encapsulation in phase-separated nanoparticles. The development of this family of optical fibers was driven by this requirement: the particles must be as small as possible to avoid light scattering. However, recent studies discussed in this article tend to disapprove this doxa. First, we present the fabrication process of such fibers, emphasizing the drawing step as a process to control the shape and size of the nanoparticles. Then, we discuss on the characterization of the composition of these nanoparticles at the nm-scale. To reach this goal, we took advantage of a recent technology: Atom Probe Tomography. These results will be compared with molecular dynamics simulations. We demonstrate that the phase-separated nanoparticle composition and therefore the chemical environment of the encapsulated RE ions is nanoparticles size dependent. As a consequence, the smallest nanoparticles, promoted by the doxa, would offer limited alteration of the luminescent properties. Finally, light scattering is not only an issue but is also an opportunity to develop new temperature, strain, refractive index multiplexed optical fiber sensors.

Using molecular dynamics simulations, we compare the motion of a nanoswimmer based on Purcell’s suggested motor with a time asymmetrical cycle with the motion of the same molecular motor with a time symmetrical cycle. We show that Purcell’s theorem still holds at the nanoscale, despite the local structure and the medium’s fluctuations. Then, with the purpose of both orienting the swimmer’s displacement and increasing the breakdown of the theorem, we study the effect of an electric field on a polarized version of these swimmers. For small and large fields, the time asymmetrical swimmer is more efficient, as suggested by Purcell. However, we find a field range for which Purcell’s theorem is broken for the time symmetric motor. Results suggest that the breakdown of the theorem arises from the competition of the orientation field and Brownian forces, while for larger fields, the field destroys the effect of fluctuations restoring the theorem.Using molecular dynamics simulations, we compare the motion of a nanoswimmer based on Purcell’s suggested motor with a time asymmetrical cycle with the motion of the same molecular motor with a time symmetrical cycle. We show that Purcell’s theorem still holds at the nanoscale, despite the local structure and the medium’s fluctuations. Then, with the purpose of both orienting the swimmer’s displacement and increasing the breakdown of the theorem, we study the effect of an electric field on a polarized version of these swimmers. For small and large fields, the time asymmetrical swimmer is more efficient, as suggested by Purcell. However, we find a field range for which Purcell’s theorem is broken for the time symmetric motor. Results suggest that the breakdown of the theorem arises from the competition of the orientation field and Brownian forces, while for larger fields, the field destroys the effect of fluctuations restoring the theorem.

This paper presents some studies on the organic heterostructures realized by Matrix Assisted Pulsed Laser Evaporation in both bi-layer and mixed layer configurations on glass substrates covered by flat or nano-patterned ITO. The donor, a star-shaped arylenevinylene compound, 4,4′,4″-tris[(4′-diphenylamino) styryl] triphenylamine, and acceptor, a non-fullerene compound, N,N′-bis-(1-dodecyl)perylene-3,4,9,10 tetracarboxylic diimide, were blended in three weight ratios: 1:2, 1:3 and 1:4. A grating of cylindrical pillars with a periodicity of 1.1 μm has been developed by UV-Nanoimprint Lithography in a polymer layer. The shape of the nanostructures changed to cone trunk by the Pulsed Laser Deposition of ITO on this nanostructured surface. The effect of the nanostructures and composition on the optical and electrical properties of the heterostructures was analyzed. The nano-patterning affected both the UV–Vis transmission and photoluminescence through the multiple reflections inside the cavities and at interfaces and the particularities of the molecular arrangement. The patterning was preserved independently of composition, but the roughness increased with increasing acceptor amount. The I-V characteristics drawn at room temperature in dark revealed an ohmic contact behavior for all heterostructures. The nano-patterning had a similar effect on the current in the heterostructures with mixed layer (1:2) and stacked bi-layer.

Structural and morphological properties of CH3NH3PbI3 thin films deposited by spin coating, with different spin speeds on glass and ITO patterned substrates were investigated. It results that long length acicular crystals, growth parallel to substrates (>200 μm for spin speeds of 800RPM/min). For low deposition spin speed these crystals are interconnected and deposited films present a high electrical conductivity. The XRD investigations indicate the formation generally of the cubic phase, or a mixture between cubic and tetragonal phase. For compact films the absorption is high over a large range of spectral domain (from 200 nm to 2100 nm), the transmission being lower than 20% in IR and less than 15% in the visible domain. From electrical properties point of view, films are highly sensitive to light. An increase of the electrical conductivity with three order of magnitude is noticed when films are exposed to a white light of a solar simulator with an intensity of 1000 W/m2, but also an important increase is observed when films are exposed to a continuous low intensity ambient light, at least one order of magnitude in less than six seconds. This behavior is identical no matter the films thickness. The variation of the electrical conductivity at exposure to light in function of time and light intensity and the variation of the electrical conductivity in function of temperature were investigated and interpreted. The experimental results, since now, comforting the assumption of a multiband model.

Doping material with nanoparticles is increasingly used as an effective method for improving their mechanical, optical, and sturdiness properties in many fields. More specifically, effective materi...

International audience

A complete characterization from optical, morphological, electrical, photo-electrical and thermo-electrical point of view was done for PEDOT:PSS thin films and DMSO and EG sensitized PEDOT:PSS films. The studies on the electrical conductivity and electrical photoconductivity allowed the calculation of different relaxation times. The relaxation time of the electrical conductivity is of order of femtosecond and is multiplied by a factor 10 when PEDOT: PSS thin films were deposited on surfaces sensitized with DMSO and EG. Besides, the photoconduction excitation and relaxation times are of order of seconds. An increase in the relaxation photoconduction time by 2 was observed for films deposited on surfaces sensitized with DMSO and by 1.2 for films deposited on surfaces sensitized with EG. The time response of electrical conductivity after exposure to light adds supplementary knowledge for the understanding of the inertial processes, or hysteresis behavior of organic or perovskite solar cells involving PEDOT:PSS films. The electrical conductivity increases with the temperature and the use of DMSO and EG as surfactants lead to higher values of electrical conductivity and Seebeck coefficient. A better stability of the electrical conductivity with the temperature increase, was noticed for films deposited on surfaces sensitized with DMSO.

The nanometric field raises a lot of questions. One of them concerns molecular motors. Is it possible to design a device capable of moving itself inside an environment ? If so how can we characterise its motion ? Does it influence the environment ? Does the environment influence the motor’s motion ? We took an interest here to the study of several parameters such as the ratio of the motor’s relative length to the environment’s molecule length, the ratio of the motor’s relative mass to the environment’s molecule mass, the motor’s folding frequency, thetemperature’s influence, the motor’s orientation, the different time configurations. We showed that the motor’s relative length ratio to the environment’s molecule length, as well as the motor’s relative mass ratio to the environment’s molecule mass, have an influence on the motor’s displacement. Every motor presenting one hinge, is subject to the scallop theorem introduced by E.M. Purcell. We found a way to break this theorem by playing on the motor’s folding frequency. Then we altered our motor in order for it to possess to hinges. We studied the effect of different time configuration on the motor’s displacement. Finally we wanted to give a privileged direction to our motor by submitting it to an electrical field.; Le domaine nanométrique présente et soulève beaucoup de questions. Une d’entre elles concerne les moteurs moléculaires. Est-il possible de concevoir un système pouvant se déplacer au sein d’un milieu ? Si oui comment caractériser son déplacement ? Le déplacement a-t-il une influence sur le milieu ? Le milieu influence-t-il le déplacement du moteur ? Nous nous sommes intéressés ici à l’étude de plusieurs paramètres tels que la taille relative du moteur par rapport à la taille des molécules constituant l’environnement, la masse relative du moteur par rapport à la masse des molécules constituant l’environnement, la vitesse des battements du moteur, l’influence de la température,l’orientation du moteur, les configurations temporelles possibles.Nous avons montré que le ratio de masse relative au moteur et des molécules du milieu, tout comme le ratio des tailles, influencent le déplacement du moteur. Tout moteur avec une seule charnière est soumis au scallop theorem énoncé par E.M. Purcell.Nous avons trouvé un moyen de briser ce théorème en jouant sur la vitesse des battements du moteur.Nous avons ensuite modifié notre moteur pour qu’il possède deux charnières. Nous avons de nouveau étudié l’effet des différentes configurations temporelles possible sur le déplacement du moteur.Pour finir nous avons voulu donner une direction privilégié à notre moteur en le soumettant à un champ électrique.

The nanometric field raises a lot of questions. One of them concerns molecular motors. Is it possible to design a device capable of moving itself inside an environment ? If so how can we characterise its motion ? Does it influence the environment ? Does the environment influence the motor’s motion ? We took an interest here to the study of several parameters such as the ratio of the motor’s relative length to the environment’s molecule length, the ratio of the motor’s relative mass to the environment’s molecule mass, the motor’s folding frequency, thetemperature’s influence, the motor’s orientation, the different time configurations. We showed that the motor’s relative length ratio to the environment’s molecule length, as well as the motor’s relative mass ratio to the environment’s molecule mass, have an influence on the motor’s displacement. Every motor presenting one hinge, is subject to the scallop theorem introduced by E.M. Purcell. We found a way to break this theorem by playing on the motor’s folding frequency. Then we altered our motor in order for it to possess to hinges. We studied the effect of different time configuration on the motor’s displacement. Finally we wanted to give a privileged direction to our motor by submitting it to an electrical field.; Le domaine nanométrique présente et soulève beaucoup de questions. Une d’entre elles concerne les moteurs moléculaires. Est-il possible de concevoir un système pouvant se déplacer au sein d’un milieu ? Si oui comment caractériser son déplacement ? Le déplacement a-t-il une influence sur le milieu ? Le milieu influence-t-il le déplacement du moteur ? Nous nous sommes intéressés ici à l’étude de plusieurs paramètres tels que la taille relative du moteur par rapport à la taille des molécules constituant l’environnement, la masse relative du moteur par rapport à la masse des molécules constituant l’environnement, la vitesse des battements du moteur, l’influence de la température,l’orientation du moteur, les configurations temporelles possibles.Nous avons montré que le ratio de masse relative au moteur et des molécules du milieu, tout comme le ratio des tailles, influencent le déplacement du moteur. Tout moteur avec une seule charnière est soumis au scallop theorem énoncé par E.M. Purcell.Nous avons trouvé un moyen de briser ce théorème en jouant sur la vitesse des battements du moteur.Nous avons ensuite modifié notre moteur pour qu’il possède deux charnières. Nous avons de nouveau étudié l’effet des différentes configurations temporelles possible sur le déplacement du moteur.Pour finir nous avons voulu donner une direction privilégié à notre moteur en le soumettant à un champ électrique.

International audience

International audience

We explore the effective nonlinear (NL) optical response of transparent materials illuminated by strong light beams with two different setups to study the influence of the numerical aperture (NA) corresponding to the collecting lens on the measured coefficients in the open and closed aperture Z-scan transmittance. For that, we have reproduced experiments in CS 2 at 532nm in the picosecond regime using D4σ-Z-scan method. It is found that measurement of high order NL coefficients is possible up to a limit defined by the self-focusing of light inside the cell and that stimulated light scattering is not significant to explain alone the saturation behaviour that occurs in the NL refraction measurements. Indications are given for future Z-scan based experiments that may clarify the new boundary conditions to be respected for the measurement.

The success of glass photonics are many, with a large spectrum of applications covering Information and Communication Technology, Health and Biology, Structural Engineering, and Environment Monitoring Systems, etc. A paradigmatic example is the development of the Erbium-Doped Fiber Amplifier (EDFA) allowing the raise of optical telecommunications and high speed internet. Silica glass is the most common glass used for photonics applications. However, certain of its characteristics may be detrimental for luminescence properties (low rare-earth solubility, high phonon energy, etc). To overcome these limitations, the use of nanoparticles in optical waveguides has gained large interest in modern photonic technology nowadays. Such waveguides would combine the advantages of silica (transparency, cost, chemical and mechanical durability, etc.) and the specific properties provided by the nanoparticles which encapsulate the rare-earth ions. In this paper, we discuss on the opportunities offered by the nanoparticles addition in glasses for lasers and amplifiers thanks to the engineering of the spectroscopic properties. We present also an emerging application: sensors based on high scattered fibers.

By means of Molecular Dynamics simulations, rare-earth-doped nanoparticles are formed in situ through phase separation mechanism within MgO-SiO 2 binary melt using a simple adaptive interatomic potential. The simulated preforms are doped with Eu3+ and Er3+ ions, and are then deformed into a fiber while glass flow effects (thermodynamical and rheological) leads to modifications of the nanoparticle's morphology. In this study, we highlight a rare-earth encapsulation in Mg-silicate nanoparticles more efficient for Er3+ ions than for Eu3+ ions. Moreover, the MgO concentration seems to converge toward a maximum value when the nanoparticles grow. Finally, preliminary results concerning the influence of the drawing parameters (temperature, elongation velocity) on the size’s distribution and on the morphology of the nanoparticles are also presented.

We investigate the dynamical behavior of a self-pulsing laser under the influence of stimulated Brillouin scattering (SBS), a system which has previously been shown to favor extreme statistics. Using a laser model coupling a multi-Stokes Brillouin scattering process with the population inversion formalism for the gain and taking into account saturable absorption effects, we demonstrate that different statistical distribution types arise as the nonlinear interactions between the laser and higher-order SBS waves lead to the occurrence of high intensity short pulses. By taking into account up to five Stokes orders, we show that highly skewed statistics and pulses with extreme peak intensities can be obtained, allowing us to describe more accurately the experimental observations and to better apprehend the underlying physics. We also unexpectedly demonstrate that the acoustic noise does not affect the emergence of such extreme events.

International audience; Hawking radiation [1], the spontaneous emission of radiation by a black hole, is one of the most important discoveries of the XXth century, uniting gravity and thermodynamics, and providing a key insight into the as yet undiscovered theory of quantum gravity. In 1981, Unruh showed that analogs of Hawking radiation could be found in material systems in which a background flow induces an effective horizon for the quasi-particles [2]. The possibility of demonstrating Hawking-like radiation in optics [3] has attracted much attention. The idea is that a short pulse induces, through the Kerr nonlinearity, a refractive index change δ n which gives rise to an effective horizon for a probe wave at another frequency. Despite considerable progress, both theoretical and experimental [4,5], demonstration of Hawking-like radiation in optics remains elusive because of the requirement of an ultra-high peak power and ultra-short background pulse, combined with the expected smallness of the rate of pair production.

Graphene quantum dots (GQDs), which are elongated strips of few-layer of graphene with straight edges attract a lot of attention for their wide potential applications, mainly because of their photoluminescence properties [1]. In addition, GQDs could inherit from both the rich nonlinear (NL) optical properties of graphene as well as the control and the versatility offered by the quantum dots. However, NL characterizations of such structures remain scarce. Here we characterize experimentally in the picosecond regime the NL refractive index and the NL absorption of blue-luminescent GQDs in solution, in the ultraviolet, visible and infrared domains [2].

International audience

International audience

International audience; An enhancement of the spectroscopic performance of rare-earth-doped silica optical fibers is still required for new photonics applications. An interesting route to tailor their optical behavior consists in embedding rare-earth ions within dielectric nanoparticles in the core of optical fibers. Experimentally, such nanoparticles can be produced in situ through spontaneous phase separation phenomenon within a MgO-SiO2 binary melt, during melt/quench sequences of MCVD fabrication process of the preform 1,2. Then, fibers are obtained by drawing at high temperature a preform containing nanoparticles. First report on the drawing process reveals an elongation of the nanoparticles in the drawing direction as well as a breakup of the larger ones 3. In this Molecular dynamics study, we use a new simple transferable model 4 to show that phase separation occurring in the MgO-SiO2 binary melt leads to the separation of liquid phases with mixed composition: Si-rich Mg-poor phases on one hand, Mg-rich Si-poor phases on the other hand. These latter phases, the so-called nanoparticles, are amorphous, non-spherical and exhibit a wide range of sizes. Mg-O coordination and MgO content increase with the nanoparticle size. With rare-earth doping, the larger nanoparticles are over-concentrated in luminescent ions. We show that the rare-earth clustering effect is prevented, compared with a pure silica matrix. Finally, at high temperature, we apply a uniaxial elongation to the nanostructured preform to mimic the experimental drawing step leading to the fiber. We report here on the effects of this drawing process on the nanoparticles characteristics.

International audience; (< 1500 characters): The study of amorphous phase-separated Dielectric Nano-Particles (DNPs) smaller than 10 nm is a great challenge for the materials community. In conjunction with Transmission Electron Microscopy (TEM) and Electron-Probe Micro-Analysis (EPMA), we took advantage of a recent technology, Tri-Dimensional (3D) Atom Probe Tomography (APT) to investigate the variations of the chemical composition in sub-20-nm oxide nanoparticles, grown in silicate glass through heat treatments, at their early stages of nucleation. More precisely, we are investigating the core of an optical fiber drawn from a preform prepared according to the Modified Chemical Vapor Deposition (MCVD) process. We provide here a comprehensive set of experimental data obtained from direct measurements of the concentration for P, Mg, Ge and Er within amorphous dielectric nanoparticles (DNP) of radii ranging from 1 nm to 10 nm. We report on an increase of the concentration of Mg and P with the size of the DNPs. Most importantly, we also demonstrate that erbium ions are partitioned in these small DNPs and their environment changes with the size of the nanoparticles. Molecular dynamics simulations were also implemented to discuss the structural modifications of the Er environment. This presentation highlights the trade off on the size of the DNPs: smaller to reduce light scattering vs bigger to modify luminescence properties.