Nanoscale mapping and control of antenna-coupling strength for bright single photon sources

Cavity QED is the art of enhancing light-matter interaction of photon emitters in cavities, with opportunities for sensing, quantum information and energy capture technologies. To boost emitter-cavity interaction, i.e. coupling strength , ultrahigh quality cavities have been concocted yielding photon trapping times of µs to ms. However, such high-Q cavities give poor photon output, hindering applications. To preserve high photon output it is advantageous to strive for highly localised electric fields in radiatively lossy cavities. Nanophotonic antennas are ideal candidates combining low-Q factors with deeply localised mode volumes, allowing large , provided the emitter is positioned exactly right inside the nanoscale mode volume. Here, with nanometre resolution, we map and tune the coupling strength between a dipole nanoantenna-cavity and a single molecule, obtaining a coupling rate of max ~ 200 GHz. Together with accelerated single photon output, this provides ideal conditions for fast and pure non-classical single photon emission with brightness exceeding 10E9 photons/sec. Clearly, nanoantennas acting as “bad” cavities offer an optimal regime for strong coupling , to deliver bright on-demand and ultrafast single photon nanosources for quantum technologies.Peer ReviewedPostprint (author's final draft

Long-range, Seamless Traffic Density Monitoring using Fibre Optic Acoustic Sensing

Accurate real-time traffic sensing is of key importance, especially in the urban environment to be able to optimise traffic flow by intelligent traffic systems (ITS). Often the high density of traffic sensors, needed to achieve an accurate real-time monitoring of important arterial roads, is difficult to implement due to technical contraints or because of high installation cost. Furthermore, existing traffic sensing technology uses sensors that are only able to measure traffic flow on a cross-section of the road where they are installed (typically on a junction), giving no information on the situation in between. An alternative "seamless" measuring technology, is to use floating car data, with Google Maps being the most prominant example. This technology allows to derive traffic information over wide road sections, however it is unable to deliver real- time information, and it relies on the “cooperation” of the data providers (the fleet owner or the mobile phone users). Fiber optic acoustic sensing (FOAS) is a new alternative technology that allows a seamless, real-time monitoring of the road traffic situation over large distances of up to 50 km using the existing telecom fiber optic cable infrastructure. In our previous work we presented an algorithm and results for traffic flow and average speed computation from FOAS raw data at a specific location along a highway and compared it to reference traffic data [1],[2]. In this paper we demonstrate the potential of the seamless nature of the technique by evaluating the traffic density over a length of 25 km of the monitored highway for different days and times of the day

Dynamique thermique et vibrationnelle de nanoparticules d'or et Au@SiO2 en régime femtoseconde : effet de la nanostructuration

Généralement, un bon conducteur thermique est aussi bon conducteur électrique (Wiedemann-Franz). Pour de nombreuses applications, il est impératif de pouvoir découpler ces deux propriétés. La nanostructuration permet de modeler les propriétés thermiques sans affecter les propriétés électriques. Lors de cette thèse, nous nous sommes intéressés à la synthèse et à la caractérisation d'un matériau initialement isolant dans lequel est insérée une assemblée de nanoparticules métalliques. Le nanocomposite élaboré est constitué de nanoparticules cœur@écorce (Au@SiO2 ou Au@Thiol) structurées en opale par méthode de type "Langmuir". Lorsque la concentration en nanoparticules est suffisante, une amplification du transfert thermique dans le nanocomposite est prédite par certains auteurs. Le couplage par rayonnement en champ proche, majoritairement plasmonique, constitue un nouveau mécanisme de transport de chaleur. Dans ce travail, nous avons étudié le transfert d'énergie au sein de nanoparticules isolées et sous forme de réseau. Dans un premier temps, nous présentons les techniques de synthèse chimique mises en œuvre pour la conception des nanocomposites et détaillons leurs propriétés optiques. Puis, nous présentons la conception du banc de mesure, il s'agit d'un banc d'imagerie pompe-sonde femtoseconde accordable en longueur d'onde permettant des études en réflexion et transmission. Les expériences que nous avons menées nous ont permis d'étudier la dynamique thermique électronique de nanoparticules d'or pour différents environnements et de mettre en évidence expérimentalement des modes de vibration acoustiques de systèmes cœur-écorce lorsqu'ils sont soumis à une excitation laser femtoseconde.Typically, a good thermal conductor is also a good electrical conductor (Wiedemann-Franz). For several applications, it is imperative to be able to decouple these two properties. Nanostructuration allows for the modification of thermal properties without affecting electrical properties. This thesis is concerned with the synthesis and characterization of nanocomposites made from an insulating matrix impregnated with metallic nanoparticles. The elaborated nanocomposite is assembled from core@shell nanoparticles (Au@SiO2 or Au@Thiol) structured in an artificial opal by the "Langmuir" method. When the nanoparticle concentration is sufficiently high, certain authors predict an amplification of thermal transport in the nanocomposite. The radiative near-field coupling, largely plasmonic, constitutes a new mechanism for heat transport. In this work, we have studied the energy transfer within isolated nanoparticles and in arrays. First, we present chemical synthesis techniques used for the nanocomposites conception and detailed their optical properties. Then, we present the conception of the experimental set-up; a multicolor femtosecond pump-probe Imaging system permitting studies in reflection or transmission. These experiments permit us to study the electronic temperature dynamics of gold nanoparticles in different environments and to measure core@shell system's acoustic vibrational modes femtosecond laser excitation

Dynamique thermique et vibrationnelle de nanoparticules d'or et Au@SiO2 en régime femtoseconde : effet de la nanostructuration

Généralement, un bon conducteur thermique est aussi bon conducteur électrique (Wiedemann-Franz). Pour de nombreuses applications, il est impératif de pouvoir découpler ces deux propriétés. La nanostructuration permet de modeler les propriétés thermiques sans affecter les propriétés électriques. Lors de cette thèse, nous nous sommes intéressés à la synthèse et à la caractérisation d'un matériau initialement isolant dans lequel est insérée une assemblée de nanoparticules métalliques. Le nanocomposite élaboré est constitué de nanoparticules cœur@écorce (Au@SiO2 ou Au@Thiol) structurées en opale par méthode de type "Langmuir". Lorsque la concentration en nanoparticules est suffisante, une amplification du transfert thermique dans le nanocomposite est prédite par certains auteurs. Le couplage par rayonnement en champ proche, majoritairement plasmonique, constitue un nouveau mécanisme de transport de chaleur. Dans ce travail, nous avons étudié le transfert d'énergie au sein de nanoparticules isolées et sous forme de réseau. Dans un premier temps, nous présentons les techniques de synthèse chimique mises en œuvre pour la conception des nanocomposites et détaillons leurs propriétés optiques. Puis, nous présentons la conception du banc de mesure, il s'agit d'un banc d'imagerie pompe-sonde femtoseconde accordable en longueur d'onde permettant des études en réflexion et transmission. Les expériences que nous avons menées nous ont permis d'étudier la dynamique thermique électronique de nanoparticules d'or pour différents environnements et de mettre en évidence expérimentalement des modes de vibration acoustiques de systèmes cœur-écorce lorsqu'ils sont soumis à une excitation laser femtoseconde.Typically, a good thermal conductor is also a good electrical conductor (Wiedemann-Franz). For several applications, it is imperative to be able to decouple these two properties. Nanostructuration allows for the modification of thermal properties without affecting electrical properties. This thesis is concerned with the synthesis and characterization of nanocomposites made from an insulating matrix impregnated with metallic nanoparticles. The elaborated nanocomposite is assembled from core@shell nanoparticles (Au@SiO2 or Au@Thiol) structured in an artificial opal by the "Langmuir" method. When the nanoparticle concentration is sufficiently high, certain authors predict an amplification of thermal transport in the nanocomposite. The radiative near-field coupling, largely plasmonic, constitutes a new mechanism for heat transport. In this work, we have studied the energy transfer within isolated nanoparticles and in arrays. First, we present chemical synthesis techniques used for the nanocomposites conception and detailed their optical properties. Then, we present the conception of the experimental set-up; a multicolor femtosecond pump-probe Imaging system permitting studies in reflection or transmission. These experiments permit us to study the electronic temperature dynamics of gold nanoparticles in different environments and to measure core@shell system's acoustic vibrational modes femtosecond laser excitation

Preliminary assessment of ship detection and trajectory evaluation using distributed acoustic sensing on an optical fiber telecom cable

International audienc

Optoacoustic response of a single submicronic gold particle revealed by the picosecond ultrasonics technique

The optoacoustic response of a single submicron (430 nm) gold particle embedded in a silica thin film is experimentally revealed by femtosecond pump-probe experiments. A semianalytical model is developed to calculate the transient reflectivity accounting for optical index changes in both media and for particle and film surface displacements. The displacement of the particle-film interface turns out to be the major contribution to the measured signal. The amplitude of the acoustical component of the transient reflectivity is modulated by the depth at which the particle is buried in the film.Etude de l'amplification de la Conduction Thermique dans des Réseaux de Nanoparticule

Far-field control of nanoscale hotspots by near-field interference

Optical nanoantennas coherently scatter incident optical radiation, creating a localized electromagnetic near-field imprinted with subwavelength phase distribution, rapidly changing in space. The nanostructuring of phase by a nanoantenna makes the scattered field locally interfere with the incident far-field, whose phase lacks nanostructuring and depends only on wave propagation in time and space. Depending on the resonance conditions and material properties, the interference strongly modifies the resultant near-field intensity of the nanoantenna. Here, we present direct imaging of the local near-field interference effect in the near-field of a resonant dipole nanoantenna, supported by numerical calculations. We use single fluorescent emitters as local detectors to map the field distribution of nanoantennas with nanometer precision in the presence of an incident field. Taking advantage of the dipole orientation of the molecule we probe the vectorial character of the near-field interference map. Exploiting the local interference we demonstrate position control of the localized field, i.e., the plasmonic hotspots in the near-field of a nanoantenna. The results shown in this paper are important for applications where the enhancement and precise hotspot position at the nanoantenna are crucial, such as in high-resolution fluorescence imaging. Moreover, the interference effect can be exploited to shape the nanoantenna near-field to produce a tailored optical response such as polarization-controlled nanoscale hotspot switching, as we show here.Peer ReviewedPostprint (author's final draft

Heterodyne picosecond thermoreflectance applied to nanoscale thermal metrology

Picosecond thermoreflectance is an unprecedented powerful technique for nanoscale heat transfer analysis and metrology, but different sources of artifacts were reported in the literature making this technique difficult to use for long delay (several ns) thermal analysis. We present in this paper a new heterodyne picosecond thermoreflectance (HPTR) technique. As it uses two slightly frequency shifted lasers instead of a mechanical translation stage, it is possible to avoid all artifacts leading to erroneous thermal parameter identifications. The principle and set-up are described as well as the model. The signal delivered by the HPTR experiment is calculated for each excitation configurations, modulating or not the pump beam. We demonstrate the accuracy of the technique in the identification of the thermal conductivity of a 50 nm thick SiO(2) layer. Then, we discuss the role of the modulation frequency for nanoscale heat transfer analysis. (C) 2011 American Institute of Physics. [doi:10.1063/1.3665129

Ultrafast stimulated emission microscopy of single nanocrystals

Single-molecule detection is a powerful method used to distinguish different species and follow time trajectories within the ensemble average. However, such detection capability requires efficient emitters and is prone to photobleaching, and the slow, nanosecond spontaneous emission process only reports on the lowest excited state. We demonstrate direct detection of stimulated emission from individual colloidal nanocrystals at room temperature while simultaneously recording the depleted spontaneous emission, enabling us to trace the carrier population through the entire photocycle. By capturing the femtosecond evolution of the stimulated emission signal, together with the nanosecond fluorescence, we can disentangle the ultrafast charge trajectories in the excited state and determine the populations that experience stimulated emission, spontaneous emission, and excited-state absorption processes

Seamless Distributed Traffic Monitoring by Distributed Acoustic Sensing (DAS) using existing Fiber Optic Cable Infrastructure

Accurate real-time traffic sensing is of key importance, especially in the urban environment to be able to optimize traffic flow by intelligent traffic systems (ITS). Often the high density of traffic sensors, needed to achieve an accurate real-time monitoring of important arterial roads, is difficult to implement due to technical contraints or because of installation cost. Furthermore, existing traffic sensing technology uses sensors that are only able to measure traffic flow on a cross-section of the road where they are installed (typically on a junction), giving no information on the situation in between. An alternative "seamless" measuring technology, is to use floating car data, with Google Maps being the most prominant example. This technology allows to derive traffic information over wide road sections, however it is unable to deliver real-time information, and it relies on the "cooperation" of the data providers (the fleet owner or the mobile phone users). Distributed acoustic sensing (DAS) is a relatively new technology that allows a seamless, real-time monitoring of the road traffic situation over large distances of up to 50 km using the existing telecom fiber optic cable infrastructure. We present first result of traffic speed estimation performed on a real highway with DAS, over a distance of 19 km and compare them to reference measurements from induction loops