<p>Investigation of laser-matter interaction has been an important research topic which is closely related to applications in various fields including industry, military, electronics, photonics, etc. With the advent of ultrafast transmission electron microscope (UTEM), in situ investigation of the interaction between pulsed laser and nanostructured materials becomes accessible, with unprecedented spatial and temporal resolution. Here, we studied two categories of materials with the help of UTEM, namely, energetic materials and plasmonic nanostructures. The results demonstrate that UTEM provides a novel and convenient way for the investigation the structural and morphological change of energetic materials under external stimuli at nanoscale. Also, UTEM makes it possible to visualize the light-induced welding between plasmonic nanostructures at real time, which helps to reveal more details about the mechanisms involved. Furthermore, we studied the formation of some novel structures by combing different gold and silver nanostructure.</p>

L’objet de cette étude concerne l’exploration, à la fois sur le plan théorique et expérimental, de la possibilité d’utilisation des métamatériaux pour des applications dans le domaine de la photonique aux longueurs d’onde télécoms (λ=1.5µm). L’un des principaux objectifs adressés dans le cadre de la thèse est de réaliser l’ingénierie de l’indice effectif en utilisant des résonances des plasmons de surface localisés des métamatériaux métallo-diélectriques. Deux cas particulièrement importants du point de vue de la réalisation technologique sont considérés :• Propagation en espace libre quand une onde lumineuse sous incidence normale ou oblique interagit avec une surface diélectrique recouverte d’une monocouche de métamatériaux.• Propagation dans une configuration guide d’onde avec une monocouche de métamatériaux à la surface d’un guide d’onde en Silicium.Les résultats des modélisations et des mesures expérimentales montrent que les propriétés optiques d’une mono-couche de métamatériau peuvent être décrites par celle d’une couche homogène avec un certain indice effectif. L’épaisseur de cette couche est égale à celle des motifs métalliques, à condition qu’elle soit inférieure à quelques dizaines de nm. Pour des faibles facteurs de remplissage en surface, l’indice de réfraction d’une telle couche suit l’approximation de Maxwell-Garnett. Cet indice effectif ne dépend pas de l’angle d’incidence ni de l’orientation de la polarisation de la lumière (perpendiculaire ou dans le plan d’incidence). Au voisinage de la fréquence de résonance pour un facteur de remplissage de métamatériau de 20% en surface on obtient un indice de réfraction très élevé : neff=10. Cet indice de réfraction est plusieurs fois supérieur à celui qu’on trouve dans des matériaux naturels. L’adaptation de cette approche à configuration guidée à utiliser une structure hybride composée d’une couche de métamatériau à la surface d’un guide d’onde en Silicium. Les travaux réalisés ont permis de démontrer la possibilité d’effectuer l’ingénierie de l’indice effectif et de contrôler le niveau des pertes d’un tel guide d’onde hybride en utilisant des métamatériau métallo-diélectriques à base des fils d’Au de 200X50X50nm. Le contraste d’indice au voisinage de la ligne de la résonance donné par des modélisations et confirmé expérimentalement est de ±1.5, soit plus que ce que l’on peut obtenir avec un guide Silicium gravé. Ce résultat représente une première démonstration sur le plan international de fonctionnement des métamatériaux en configuration guidée.De plus, en contrôlant l’orientation des motifs de métamatériaux, on peut réaliser un indice anisotrope. Les résultats obtenus ouvrent des perspectives très prometteuses pour la réalisation de dispositifs en optique guidée utilisant les transformations d’espace. / The subject of the PhD thesis deals with metamaterials for photonic applications. The main objective is to investigate the potential of metallic metamaterials for building optical functions at NIR optical frequencies. A significant part of the work is focused on the engineering of the metamaterials effective index associated with localized plasmon resonances. Two configurations of particular importance for fabrication technology are considered:• Free space light propagation, with the incident electromagnetic wave interacting with single metafilms at either normal or oblique incidence. • Guided wave configuration, with single metamaterial layer placed on top of dielectric waveguide.For the free space configuration, the validity of the effective medium approach was investigated both numerically and experimentally with the example of metamaterials composed of either gold cut wires or split ring resonators and continuous wires on silicon substrate. On the basis of these examples it was shown that the metafilm behavior is indeed analogous to that of a homogeneous layer. The thickness of this layer is that of the deposited metal. The validity of this conclusion was verified with respect to a number of criteria consistent with the Maxwell-Garnett approximation. It was shown in particular that near the resonance frequency the effective index of the metafilm layer can reach very high values neff=10 that cannot be attained with natural materials.The effective medium approach developed for a single metamaterial layer in free space configuration was further extended to a guided wave configuration. The objective is to achieve an efficient control over the flow of light in the waveguide using effective index variations induced by metamatarial resonances. The possibility of achieving a significant effective index variation with a silicon slab waveguide covered by 200X50X50nm cut wires was investigated by numerical modeling and confirmed by experimental results. The magnitude of local index variation in the vicinity of the resonance frequency deduced from experimental data is as high as ±1.5. The possibility for controlling the local effective index at the nanoscale can be used in transformation optics applications. The hybrid metamaterial guided wave configuration may become a promising alternative to the bulk multi-layers metamaterial structures in the near infrared domain.

Ce travail vise à concevoir un modulateur optique assisté par plamsons, compatible CMOS et à faible consommation électrique. L’électro-absorption, basée sur l’effet Franz-Keldysh dans le germanium, a été choisie comme principe de modulation pour réduire la taille du dispositif et la consommation d'énergie électrique associée. L’effet Franz-Keldysh se traduit par un changement du coefficient d'absorption du matériau près du bord de bande sous l'application d'un champ électrique statique, d'où la production d'une modulation directe de l'intensité lumineuse. L'utilisation de plasmons permet en principe d’augmenter l'effet électro-optique en raison du fort confinement du mode optique. Un outil de simulation électro-optique intégré a été développé pour concevoir et optimiser le modulateur. Le modulateur plasmonique proposé a un taux d'extinction de 3.3 dB avec des pertes d'insertion de 11.2 dB et une consommation électrique de seulement 20 fJ/bit, soit la plus faible consommation électrique décrite pour les modulateurs photoniques sur silicium. Le couplage du modulateur à un guide silicium standard en entrée et en sortie a également été optimisé par l’introduction d'un adaptateur de mode Si-Ge optimisé, réduisant les pertes de couplage à seulement 1 dB par coupleur. Par ailleurs, un travail expérimental a été effectué pour tenter de déplacer l'effet Franz-Keldysh, maximum à 1650 nm, à de plus faibles longueurs d'onde proches de 1.55 μm pour des applications aux télécommunications optiques. / This work aims to design a CMOS compatible, low-electrical power consumption modulator assisted by plasmons. For compactness and reduction of the electrical power consumption, electro-absorption based on the Franz-Keldysh effect in Germanium was chosen for modulation. It consists in the change of the absorption coefficient of the material near the band edge under the application of a static electric field, hence producing a direct modulation of the light intensity. The use of plasmons allows enhancing the electro-optical effect due to the high field confinement. An integrated electro-optical simulation tool was developed to design and optimize the modulator. The designed plasmonic modulator has an extinction ratio of 3.3 dB with insertion losses of 13.2 dB and electrical power consumption as low as 20 fJ/bit, i.e. the lowest electrical power consumption reported for silicon photonic modulators. In- and out-coupling to a standard silicon waveguide was also engineered by the means of an optimized Si-Ge taper, reducing the coupling losses to only 1 dB per coupler. Besides, an experimental work was carried out to try to shift the Franz-Keldysh effect, which is maximum at 1650 nm, to lower wavelength close to 1.55 μm for telecommunication applications.

Surface plasmons are collective oscillations of free electrons excited at a metal-dielectric interface by incident light. They possess a broad set of interesting properties including a high degree of tunability, the generation of strong field enhancements close to the metal's surface and high sensitivity to their adjacent dielectric environment. It is possible to enhance the sensitivity of plasmonic systems by using narrow plasmon resonances. In this thesis two approaches to narrowing surface plasmon resonances have been studied: diffraction coupling of localised surface plasmon resonances in gold nanoarrays and the use of graphene-protected copper thin films. Applications of these approaches in hybrid systems have been considered for modulation, waveguiding, biosensing and field enhancements. Arrays of gold nanostripes fabricated on a gold sublayer have been used to create extremely narrow plasmon resonances using diffraction coupling of localised plasmon resonances with quality factors up to a value of $Q \sim 300$, among the highest reported in the literature. The nanostructures were designed to give the narrowest resonance at the telecommunication wavelength of 1.5 µm, allowing for this array geometry to be used in hybrid systems for proof-of-concept optoelectronic devices. The gold nanostripe array was used in a hybrid nanomechanical electro-optical modulator along with hexagonal boron nitride (hBN) and graphene. The modulator was fabricated with an air gap between the nanoarray and the hexagonal boron nitride/graphene. Applying a gate voltage across the device moves the hBN towards the nanoarray, resulting in broadband modulation effects from the ultraviolet through to the mid-infrared dependant on the motion of the hBN instead of graphene gating. The deposition of a 400 nm hafnium(IV) oxide film on top of the gold nanoarray created a structure capable of guiding modes at 1.5 µm. The hybrid air-dielectric-stripe waveguide is capable of guiding modes over a distance of 250 µm. Copper thin films have stronger plasmon resonances and higher phase sensitivity than gold thin films. Transferring a graphene sheet on the copper prevents oxidation of the copper. A feasibility study of this hybrid system has shown that phase-sensitive graphene-protected copper biosensing can detect HT-2 mycotoxin with over four orders of magnitude greater sensitivity than commercially-available gold-based surface plasmon resonance biosensing systems. In summary, two methods of attaining narrow plasmon resonances have been demonstrated and their promise in modulation, waveguiding and biosensing have been demonstrated.

Le transfert d'énergie par résonance de type Förster (FRET) permet de mesurer des distances nanométriques grâce à la dépendance critique de l'efficacité du transfert avec la séparation entre un donneur et un accepteur d'énergie. Le phénomène se produit quand le fluorophore donneur dans l'état excité transfère son énergie d'excitation à un accepteur à proximité de façon non-radiative avec une interaction dipôle-dipôle de champ proche. Les structures nanophotoniques sont capables de contrôler cette interaction grâce à la modification de la densité local d'états électromagnétiques (LDOS) d'un émetteur quantique. Nous avons démontré clairement l'exaltation du transfert d'énergie des paires FRET individuelles sous l'influence des nano-ouvertures percées en or et en aluminium et aussi à l'aide des designs plus complexes comme la `` antenna-in-box ". Notamment, nous avons dévoilé l'importance essentielle de l'orientation relative entre les dipôles sur les possibilités d'exaltation du transfert d'énergie par le biais des nanostructures. Également, nous avons utilisé des nanofils en argent pour démontrer un transfert d'énergie de long-distance entre deux nanoparticles séparées de plus d'un micromètre. Nos résultats éclairent le chemin de l'exploration du FRET, qui est largement utilisé dans les sciences du vivant et la biotechnologie. Les nanostructures optiques ouvrent de plus des perspectives d'applications innovantes pour la construction de biocapteurs, de sources de lumière ou dans l'industrie photovoltaïque. / The technique of Förster resonance energy transfer (FRET) determines the separation between two molecules at the nanometer scale, where molecular interactions can take place. The phenomenon requires a donor fluorophore transferring its energy in a non-radiative way, through a near-field dipole-dipole interaction, to an acceptor. Nanophotonics achieves accurate control over these interactions by modifying the local density of optical states (LDOS) of a single quantum emitter. We have clearly demonstrated enhanced energy transfer within single FRET pairs confined in single nanoapertures made of gold and also aluminum or in more complex structures like the antenna-in-box design. In particular, we have revealed the strong influence of the mutual dipole orientation on the FRET enhancement using nanostructures. Also, by means of silver nanowires, we have demonstrated a long-range plasmon-mediated fluorescence energy transfer between two nanoparticles separated by micrometer distance. Our results are clearing a new path to improve the energy transfer process widely used in life sciences and biotechnology. Optical nanostructures open up many potential applications for biosensors, light sources or photovoltaics.

Na presente tese de doutorado, foram exploradas possibilidades para a aplicação de nanopartículas (NPs) metálicas plasmônicas (fenômenos ópticos intensificados) em processos de fotocatálise e em células solares de Si. Estratégias foram exploradas para a imobilização das NPs plasmônicas em TiO2 Degussa P25 (mistura anatase:rutila 4:1) para captação da radiação eletromagnética UV/visível e somente visível em processos fotocatalíticos; e de NPs de Cu em células solares de Si para processos de fotoconversão, contribuindo com a compreensão dos fenômenos de intensificação local de energia mediados pelas NPs, o qual ainda está em debate no cenário científico. Compósitos de P25+NPs Ag de diferentes arquiteturas (fios, esferas e fotorreduzidas), de P25+NPs Ag recoberta com uma camada de SiO2 e de P25+NPs Au foram desenvolvidos. A caracterização dos materiais foi realizada por meio de técnicas de espectroscopia UV-VIS, IR e Raman, área superficial, DRX e de microscopia eletrônica de varredura e de transmissão. Os efeitos das propriedades plasmônicas dessas nanopartículas foram avaliados na eficiência de fotodegradação de três corantes (alizarina vermelha S, vermelho do Congo e fenossafranina) e de fenol. Todos os materiais plasmônicos apresentaram bom desempenho catalítico, aumentando consideravelmente a velocidade e a porcentagem de fotodegradação sob radiação UV/visível, mas principalmente sob radiação visível (onde a fotodegradação catalisada por P25 é limitada). A comparação entre a fotodegradação de fenol pelo compósito P25+NPs Ag esferas e P25+NPs Ag@SiO2 permitiu concluir que a transferência de carga não é o fenômeno que governa o aumento da eficiência catalítica em comparação à fotodegradação catalisada por P25. O fenômeno de intensificação de radiação eletromagnética localizada por meio de LSPR foi observado também em células solares de silício de primeira geração (wafer) contendo NPs de Cu imobilizadas em sua superfície. Aumentos na densidade de corrente de curto-circuito de cerca de 8 % na região acima de 750 nm e de até 16% na potência destas células solares foram observados. / In this thesis, we explored possibilities for the application of metallic plasmonic nanoparticles (NPs) resulting in intensified optical phenomena processes in photocatalysis and Si solar cell. Different strategies were explored for the immobilization of plasmonic NPs on TiO2 Degussa P25 (mixture anatase: rutile 4:1) to capture electromagnetic radiation UV / visible and visible only in photocatalytic processes; and Cu NPs in Si solar cell for photoconversion processes, contributing with the understanding of the phenomena related to the localized ressonance energy mediated by NPs, which is still under debate in the scientific field. Composites of P25+Ag NPs of various architectures (wires, spheres and photoreduced) P25+Ag NPs coated with a layer of SiO2 and P25+Au NPs were developed. The material characterization was performed by means of UV-VIS, IR and Raman spectroscopies, BET surface area, XRD and scanning and transmission electron microscopy. The effects of plasmonic nanoparticles properties were evaluated in the photodegradation efficiency of three textile dyes (Alizarin Red S, Congo red and phenosafranine) and phenol. All plasmonic materials showed good catalytic performance, greatly increasing the kinetic and percentage of photodegradation under UV/visible, but mostly under visible light (where the photodegradation catalyzed by P25 is limited). The comparison between the photodegradation of phenol by P25+Ag sphere NPs and P25+Ag@SiO2 composite showed that the charge transfer is not the phenomenon that governs the increase in catalytic efficiency when compared to the photodegradation catalyzed by P25. The phenomenon of near field intensification through LSPR was also observed in first generation Si solar cells (wafer) containing Cu NPs immobilized on its surface. Increases in the short-circuit current density of about 8% in the region above 750 nm and up to 16% in the power of these solar cells were observed.

Plasmonics, the science of the excitation of surface plasmon polaritons (SPP) at the metal-dielectric interface under intense beam radiation, has been studied for its immense potential for developing numerous nanophotonic devices, optical circuits and lab-on-a-chip devices. The key feature, which makes the plasmonic structures promising is the ability to support strong resonances with different behaviors and tunable localized hotspots, excitable in a wide spectral range. Therefore, the fundamental understanding of light-matter interactions at subwavelength nanostructures and use of this understanding to tailor plasmonic nanostructures with the ability to sustain high-quality tunable resonant modes are essential toward the realization of highly functional devices with a wide range of applications from sensing to switching. We investigated the excitation of various plasmonic resonance modes (i.e. Fano resonances, and toroidal moments) using both optical and terahertz (THz) plasmonic metamolecules. By designing and fabricating various nanostructures, we successfully predicted, demonstrated and analyzed the excitation of plasmonic resonances, numerically and experimentally. A simple comparison between the sensitivity and lineshape quality of various optically driven resonances reveals that nonradiative toroidal moments are exotic plasmonic modes with strong sensitivity to environmental perturbations. Employing toroidal plasmonic metasurfaces, we demonstrated ultrafast plasmonic switches and highly sensitive sensors. Focusing on the biomedical applications of toroidal moments, we developed plasmonic metamaterials for fast and cost-effective infection diagnosis using the THz range of the spectrum. We used the exotic behavior of toroidal moments for the identification of Zika-virus (ZIKV) envelope proteins as the infectious nano-agents through two protocols: 1) direct biding of targeted biomarkers to the plasmonic metasurfaces, and 2) attaching gold nanoparticles to the plasmonic metasurfaces and binding the proteins to the particles to enhance the sensitivity. This led to developing ultrasensitive THz plasmonic metasensors for detection of nanoscale and low-molecular-weight biomarkers at the picomolar range of concentration. In summary, by using high-quality and pronounced toroidal moments as sensitive resonances, we have successfully designed, fabricated and characterized novel plasmonic toroidal metamaterials for the detection of infectious biomarkers using different methods. The proposed approach allowed us to compare and analyze the binding properties, sensitivity, repeatability, and limit of detection of the metasensing devices

The study of optical phenomena related to the strong electromagnetic response of noble metals (silver (Ag) and gold (Au) being most popular) over the last couple of decades has led to the emergence of a fast growing research area called plasmonics named after 'surface plasmons' which are electron density waves that propagate along the interface of a metal and a dielectric medium. Surface plasmons are formed by the coupling of light to the electrons on the metal surface subject to the fulfillment of certain physical conditions and they are bound to the metal surface. Depending on whether the metallic medium is a continuous film or a structure having dimensions less than or comparable to the wavelength of the exciting light, propagating or localized surface plasmons can be excited. The structure can be either a hole or an arbitrary pattern in a metal film, or a metallic particle. An array of subwavelength structures can behave as an effective homogeneous medium to incident light and this is the basis of a new class of media known as metamaterials. Metallic metamaterials enable one to engineer the electromagnetic response to  incident light and provide unconventional optical properties like negative refractive index as one prominent example. Metamaterials exhibiting negative index (also called negative index materials (NIMs)) open the door for super resolution imaging  and development of invisibility cloaks. However, the only problem affecting the utilization of plasmonic media to their fullest potential is the intrinsic loss of the metal, and it becomes a major issue especially at visible-near infrared (NIR) frequencies. The frequency of the surface plasmon is the same as that of the exciting light but its wavelength could be as short as that of X-rays. This property allows light of a given optical frequency to be conned into very small volumes via subwave lengthmetallic structures, that can be used to develop ecient sensors, solar cells, antennas and ultrasensitive molecular detectors to name a few applications. Also, interaction of surface plasmons excited in two or more metallic subwavelength structures in close proximity inuences the far-eld optical properties of the overall coupled system. Some eects of plasmonic interaction in certain coupled particles include polarization conversion, optical activity and transmission spectra mimicking electromagnetically-induced transparency (EIT) as observed in gas based atomicsy stems. In this thesis, we mainly focus on the optical properties of square arrays of certain plasmonic structures popularly researched in the last decade. The structures considered are as follows: (1) subwavelength holes of a composite hole-shape providing superior near-eld enhancement such as two intersecting circles (called' double hole') in an optically thick Au/Ag lm, (2) double layer shnets, (3) subwavelength U-shaped particles and (4) rectangular bars. The entire work is based on electromagnetic simulations using time and frequency domain methods. Au/Ag lms with periodic subwavelength holes provide extraordinarily high transmission of light at certain wavelengths much larger than the dimension of the perforations or holes. The spectral positions of the maxima depend on the shape of the hole and the intra-hole medium, thereby making such lms function as a refractive index sensor in the transmission mode. The sensing performance of the double-hole geometry is analyzed in detail and compared to rectangular holes. Fishnet metamaterials are highly preferred when it comes to constructing a NIM at optical frequencies. A shnet design that theoretically oers a negative refractive index with least losses at telecommunication wavelengths (1.4 1.5 microns) is presented. U-shaped subwavelength metallic particles, in particular single-slit split-ring resonators (SSRRs), provide a large negative response to the magnetic eld of light at a specic resonance frequency. The spectral positions of the structural resonances of the U-shaped particle can be found from its array far field transmission spectrum at normal incidence. An effort is made to clarify our understanding of these resonances with the help of localized surface plasmon modes excited in the overall particle. From an application point of view, it is found that a planar square array of SSRRs eectively functions as an optical half-wave waveplate at the main resonance frequency by creating a polarization in transmission that is orthogonal to that of incident light. A similar waveplate eect can be obtained purely by exploiting the near-eld interaction of dierently oriented neighbouring SSRRs. The physical reasons behind polarization conversion in dierent SSRR-array systems are discussed. A rectangular metallic bar having its dipolar resonance in the visible-NIR is called a nanoantenna, owing to its physical length in the order of nanometers. The excitation of localized surface plasmons, metal dispersion and the geometry of the rectangular nanoantenna make an analytical estimation of the physical length of the antenna from the desired dipolar resonance dicult. A practical map of simulated resonance values corresponding to a variation in geometrical parameters of Au bar is presented. A square array of a coupled plasmonic system comprising of three nanoantennas provides a net transmission response that mimicks the EIT effect. The high transmission spectral window possesses a peculiar dispersion profile that enables light with frequencies in that region to be slowed down. Two popular designs of such plasmonic EIT systems are numerically characterized and compared. / <p>QC 20121017</p>

Photonics nowadays is one of the most rapidly developing areas of modern physics. Photonic chips are considered to be promising candidates for a new generation of high-performance systems for informational technology, as the photonic devices provide much higher information capacity in comparison to conventional electronics. They also offer the possibility of integration with electronic components to provide increased functionality. Photonics has also found numerous applications in various fields including signal processing, computing, sensing, printing, and others. Photonics, which traditionally covers lasing cavities, waveguides, and photonic crystals, is now expanding to new research directions such as plasmonics and nanophotonics. Plasmonic structures, namely nanoparticles, metallic and dielectric waveguides and gratings, possess unprecedented potential to guide and manipulate light at nanoscale. This Thesis presents the results of theoretical studies of light propagation in photonic and plasmonic structures, namely lasing disk microcavities, photonic crystals, metallic gratings and nanoparticle arrays. A special emphasis has been made on development of high-performance techniques for studies of photonic devices. The following papers are included: In the first two papers (Paper I and Paper II) we developed a novel scattering matrix technique for calculation of resonant states in 2D disk microcavities with the imperfect surface or/and inhomogeneous refraction index. The results demonstrate that the surface imperfections represent the crucial factor determining the $Q$ factor of the cavity. A generalization of the scattering-matrix technique to the quantum-mecha\-nical electron scattering has been made in Paper III. This has allowed us to treat a realistic potential of quantum-corrals (which can be considered as nanoscale analogues of optical cavities) and has provided a new insight and interpretation of the experimental observations. Papers IV and V present a novel effective Green's function technique for studying light propagation in photonic crystals. Using this technique we have analyzed surface modes and proposed several novel surface-state-based devices for lasing/sensing, waveguiding and light feeding applications. In Paper VI the propagation of light in nanorod arrays has been studied. We have demonstrated that the simple Maxwell Garnett effective-medium theory cannot properly describe the coupling and clustering effects of nanorods. We have demonstrated the possibility of using nanorod arrays as high-quality polarizers. In Paper VII we modeled the plasmon-enhanced absorption in polymeric solar cells. In order to excite a plasmon we utilized a grated aluminum substrate. The increased absorption has been verified experimentally and good agreement with our theoretical data has been achieved.

The electronic structure and optical properties of metallic nanoparticles are theoretically investigated front first principles. An efficient implementation of time-dependent density functional theory allows a fully quantum mechanical description of systems large enough to display collective electron oscillations and surface plasmon modes. The results are compared with traditional classical electrodynamical approaches. Different regimes of interest are identified, both where classical electrodynamical models yield accurate descriptions, and where quantum effects are indispensable for understanding plasmonic properties in nanostructures. The limits of validity of classical electrodynamics are clearly established for the study of a variety of relevant geometries.