Light interaction with matter has long been an area of interest throughout history, spanning many fields of study. In recent decades, the investigation of light-matter interactions with nanostructures has become an intense area of research in the field of photonics. Metallic nanostructures, in particular, are of interest due to the interesting properties that arise when interacting with light. The properties are a result of the excitation of surface plasmons which are the collective oscillation of the conduction electrons in the metal. Since the conduction electrons can be thought of as harmonic oscillators, they are quantized in a similar fashion. Just as a photon is a quantum of oscillations of an electromagnetic field, the plasmon is a quantum of electron oscillations of a metal. There are three types of plasmons: 1. Bulk plasmons, also called volume plasmons, are longitudinal density fluctuations which propagate through a bulk metal with an eigenfrequency of �� called the plasma frequency. 2. Localized surface plasmons are non-propagating excitations of the conduction electrons of a metallic nanoparticle coupled to an electromagnetic field. 3. Surface plasmon polaritons are evanescent, dispersive propagating electromagnetic waves formed by a coupled state between a photon and the excitation of the surface plasmons. They propagate along the surface of a metal-dielectric interface with a broad spectrum of eigenfrequencies from � = 0 to � = ��⁄√2. iv Plasmonics is a subfield of photonics which focuses on the study of surface plasmons and the optical properties that result from light interacting with metal films and nanostructures on the deep subwavelength scale. In this thesis, plasmonic nanostructures are investigated for optical waveguides and other nanophotonic applications through computational simulations primarily base on electrodynamic theory. The theory was formulated by several key figures and established by James Clerk Maxwell after he published a set of relations which describe all classical electromagnetic phenomena, known as Maxwell’s equations. Using methods based on Maxwell’s equations, the optical properties of metallic nanostructures utilizing surface plasmons is explored. In Chapter 3, light propagation of bright and dark modes of a partially and fully illuminated silver nanorod is investigated for waveguide applications. Then, the origin of the Fano resonance line shape in the scattering spectra of a silver nanorod is investigated. Next, in Chapter 4, the reflection and transmission of a multilayer silver film is simulated to observe the effects of varying the dielectric media between the layers on light propagation. Building on the multilayer film work, metal-insulator-metal waveguides are explored by perforating holes in the bottom layer of a two layer a silver film to investigate the limits of subwavelength light trapping, confinement, and propagation. Lastly, in Chapter 5, the effect of surface plasmons on the propagation direction of electromagnetic wave around a spherical silver nanoparticle which shows an effective negative index of refraction is examined. In addition, light manipulation using a film of silver prisms with an effective negative index of refraction is also investigated. The silver prisms demonstrate v polarization selective propagation for waveguide and optical filter applications. These studies provide insight into plasmonic mechanisms utilized to overcome the diffraction limit of light. Through better understanding of how to manipulating light with plasmonic nanostructures, further advancements in nanophotonic technologies for applications such as extremely subwavelength waveguides, sensitive optical detection, optical filters, polarizers, beam splitters, optical data storage devices, high speed data transmission, and integrated subwavelength photonic circuits can be achieved.

Inspired by graphene, I investigate the properties of several different real and artificial Dirac materials. Firstly, I consider a two-dimensional honeycomb lattice of metallic nanoparticles, each supporting localised surface plasmons, and study the quantum properties of the collective plasmons resulting from the near field dipolar interaction between the nanoparticles. I analytically investigate the dispersion, the effective Hamiltonian and the eigenstates of the collective plasmons for an arbitrary orientation of the individual dipole moments. When the polarisation points close to normal to the plane the spectrum presents Dirac cones, similar to those present in the electronic band structure of graphene. I derive the effective Dirac Hamiltonian for the collective plasmons and show that the corresponding spinor eigenstates represent chiral Dirac-like massless bosonic excitations that present similar effects to those of electrons in graphene, such as a non-trivial Berry phase and the absence of backscattering from smooth inhomogeneities. I further discuss how one can manipulate the Dirac points in the Brillouin zone and open a gap in the collective plasmon dispersion by modifying the polarisation of the localized surface plasmons, paving the way for a fully tunable plasmonic analogue of graphene. I present a phase diagram of gapless and gapped phases in the collective plasmon dispersion depending on the dipole orientation. When the inversion symmetry of the honeycomb structure is broken, the collective plasmons become gapped chiral Dirac modes with an energy-dependent Berry phase. I show that this concept can be generalised to describe many real and artificial graphene-like systems, labeling them Dirac materials with a linear gapped spectrum. I also show that biased bilayer graphene is another Dirac material with an energy dependent Berry phase, but with a parabolic gapped spectrum. I analyse the relativistic phenomenon of Klein Tunneling in both types of system. The Klein paradox is one of the most counter-intuitive results from quantum electrodynamics but it has been seen experimentally to occur in both monolayer and bilayer graphene, due to the chiral nature of the Dirac quasiparticles in these materials. The non-trivial Berry phase of pi in monolayer graphene leads to remarkable effects in transmission through potential barriers, whereas there is always zero transmission at normal incidence in unbiased bilayer graphene in the npn regime. These, and many other 2D materials have attracted attention due to their possible usefulness for the next generation of nano-electronic devices, but some of their Klein tunneling results may be a hindrance to this application. I will highlight how breaking the inversion symmetry of the system allows for results that are not possible in these system's inversion symmetrical counterparts.

Malgré leurs contribution dans plusieurs domaines, les biopuces à lecture plasmonique conventionnelles basées sur l'utilisation d’un film métallique plan d'or, sont limitées en terme de sensibilité surtout quand il s'agit de détecter des molécules de faible masse molaire à l’état de trace.Dans ce cadre, nous étudions numériquement et expérimentalement le potentiel de détection d’interactions biomoléculaires d’une nouvelle génération de biopuces à lecture plasmonique intégrant un film métallique micro-nano-structurée en réseau rectangulaire 1D. L’étude numérique développée met en œuvre une méthode hybride, basée sur la combinaison de deux méthodes classiques : la méthode des éléments finis et la méthode modale de Fourier. Grâce à ce nouvel outil numérique, nous présentons une cartographie exhaustive du potentiel de détection d’une couche biologique, en variant les paramètres de la structuration liés aux dimensions du réseau. La réponse de la biopuce à l’accrochage de biomolécules est ensuite interprétée théoriquement par les différents phénomènes plasmoniques notamment les «points chauds» et les bandes plasmoniques interdites. Nos calculs soulignent l'importance de l’exploitation du confinement de la lumière à travers la structuration sub-longueur d’onde des surfaces plasmoniques. Ceci permet non seulement d’optimiser les paramètres géométriques afin d’améliorer la sensibilité vis-à-vis de la réponse d’une biopuce conventionnelle, mais aussi de mettre en évidence la transition entre le régime où les plasmons propagatifs dominent et le régime où les plasmons localisés dominent. De nouvelles figures de mérite sont introduites pour évaluer les performances des biopuces structurées.Cette étude montre également que de nouvelles opportunités pour améliorer davantage la bio-sensibilité sont offertes, si la localisation de biomolécules peut être effectuée dans les régions où le champ électrique est amplifié et confiné. / Surface plasmons resonance imaging with continuous thin metallic films have become a central tool for the study of biomolecular interactions. However, in order to extend the field of applications of surface plasmons resonance systems to the trace detection of biomolecules having low molecular weight, a change in the plasmonic sensing methodology is needed. In this study, we investigate theoretically and experimentally the sensing potential of 2D nano- and micro- ribbon grating structuration on the surface of Kretschmann-based surface plasmon resonance biosensors when they are used for detection of biomolecular binding events. Numerical simulations were carried out by employing a fast and novel model based on the hybridization of two classical methods, the Fourier Modal Method and the Finite Element Method. Our calculations confirm the importance of light manipulation by means of structuration of the plasmonic thin film surfaces on the nano- and micro- scales. Not only does it highlight the geometric parameters that allow the sensitivity enhancement, and associated figures of merit, compared with the response of the conventional surface plasmon resonance biosensor based on a flat surface, but it also describes the transition from the regime where the propagating surface plasmon mode dominates to the regime where the localized surface plasmon mode dominates. An exhaustive mapping of the biosensing potential of the nano- and micro- structured biosensors surface is presented, varying the structural parameters related to the ribbon grating dimensions. New figures of merit are introduced to evaluate the performance of the structured biosensors. The structuration also leads to the creation of regions on biosensor chips that are characterized by strongly enhanced electromagnetic fields. New opportunities for further improving the bio-sensitivity are offered if localization of biomolecules can be carried out in these regions of high electromagnetic fields enhancement and confined.

Pour la première fois, en associant un microscope à effet tunnel (STM) et un microscope optique inversé,nous avons imagé les plasmons de surface excités électriquement sur un film d’or avec la pointe d’un STM.Par microscopie de fuite radiative, en observant l’image de l’interface air/or et celle du plan de Fourierassocié, nous avons distingué les plasmons propagatifs des plasmons localisés sous la pointe. Les plasmonspropagatifs sont caractérisés par une distance de propagation et une direction d’émission en accord aveccelles de plasmons propagatifs créés par excitation laser sur des films d’or de mêmes épaisseurs. Les fuitesradiatives des plasmons localisés s’étalent jusqu’à l’angle maximum d’observation. Plasmons propagatifs etlocalisés ont une large bande spectrale dans le visible. Si la pointe est plasmonique (en argent), lesplasmons localisés ont une composante supplémentaire due au couplage associé. Pour différents types depointe, nous avons déterminé les intensités relatives des plasmons localisés et propagatifs. Nous trouvonsque chaque mode plasmon (propagatif ou localisé) peut être préférentiellement sélectionné en modifiant lematériau de la pointe et sa forme. Une pointe en argent produit une intensité élevée de plasmons localisés,tandis qu’une pointe fine de tungstène (rayon de l’apex inférieur à 100 nm) produit essentiellement desplasmons propagatifs. Nous avons étudié la cohérence spatiale des plasmons propagatifs excités par la pointe du STM. Avec un film d’or opaque (épaisseur 200 nm) percé de paires de nanotrous nous avons réalisé une expérienceanalogue à celle des fentes d’Young. Des franges d’interférences sont observées. La mesure de leurvisibilité en fonction de la distance des nanotrous donne une longueur de cohérence des plasmons de 4.7±0.5 μm. Cette valeur, très proche de la valeur 3.7± 1.2 μm déduite de la largeur de la distribution spectraledes plasmons, indique que l’élargissement spectral des plasmons propagatifs est homogène.Nous avons aussi étudié la diffusion des plasmons propagatifs excités par la pointe du STM par desnanoparticules d’or déposées sur un film d’épaisseur 50 nm. Nous observons une diffusion élastique et unediffusion radiative. Des franges d’interférences sont observées dans la région d’émission lumineuseinterdite du plan de Fourier, dont la période est inversement proportionnelle à la distancepointe-nanoparticule d’or avec un facteur de proportionnalité égal à la longueur d’onde moyenne desplasmons. Il y a donc interférence entre la radiation des plasmons localisés et la radiation provenant de ladiffusion des plasmons propagatifs sur les nanoparticules d’or. Ceci indique que les plasmons localisés etpropagatifs excités électriquement par la pointe du STM sont différentes composantes du plasmon uniqueproduit par effet tunnel inélastique avec la pointe du STM. Ces résultats originaux sur les plasmons créés sur film d’or par un effet tunnel inélastique localisé à l’échelle atomique (i) élargissent la compréhension du processus et (ii) offrent des perspectives intéressantes pour une association de la nanoélectronique et de la nanophotonique. / For the first time, using a equipment combining a scanning tunneling microscope (STM) and an invertedoptical microscope, we excite and directly image STM-excited broadband propagating surface plasmons ona thin gold film. The STM-excited propagating surface plasmons have been imaged both in real space andFourier space by leakage radiation microscopy. Broadband localized surface plasmons due to the tip-goldfilm coupled plasmon resonance have also been detected. Quantitatively, we compare the intensities ofSTM-excited propagating and localized surface plasmons obtained with different STM tips. We find that the intensity of each plasmon mode can be selectively varied by changing the STM tip shape or material composition. A silver tip produces a high intensity of localized surface plasmons whereas a sharp (radius < 100 nm) tungsten tip produces mainly propagating surface plasmons. We have investigated the coherence of STM-excited propagating surface plasmons by performingexperiments on a 200 nm thick (opaque) gold film punctured by pairs of nanoholes. This work is analogousto Young’s double-slit experiment, and shows that STM-excited propagating surface plasmons have acoherence length of 4.7±0.5 μm. This coherent length is very close to the value 3.7±1.2 μm expected fromthe spectrum, which indicates that the spectrum broadening of STM-excited surface plasmons ishomogeneous. We have also studied the in-plane and radiative scattering of STM-excited propagating surface plasmons bygold nanoparticles deposited on a 50 nm thick gold film. In the Fourier space images, interference fringesare observed in the forbidden light region. This interference occurs between STM-excited localized surfaceplasmons (radiating at large angles from the tip position) and the radiative scattering by the goldnanoparticle of STM-excited propagating surface plasmons. This indicates that STM-excited localized andpropagating surface plasmons are different components of the same single plasmon produced by inelasticelectron tunneling with the STM tip. These results not only broaden the understanding about the excitation process of STM excited surface plasmons but also offer interesting perspectives for the connection between nanoelectronics andnanophotonics.

We have developed a general theory of the plasmonic enhancement of many-body phenomena resulting in a closed expression for the surface plasmon-dressed Coulomb interaction. It is shown that this interaction has a resonant nature. We have also demonstrated that renormalized interaction is a long-ranged interaction whose intensity is considerably increased compared to bare Coulomb interaction over the entire region near the plasmonic nanostructure. We illustrate this theory by re-deriving the mirror charge potential near a metal sphere as well as the quasistatic potential behind the so-called perfect lens at the surface plasmon (SP) frequency. The dressed interaction for an important example of a metal–dielectric nanoshell is also explicitly calculated and analyzed. The renormalization and plasmonic enhancement of the Coulomb interaction is a universal effect, which affects a wide range of many-body phenomena in the vicinity of metal nanostructures: chemical reactions, scattering between charge carriers, exciton formation, Auger recombination, carrier multiplication, etc. We have described the nanoplasmonic-enhanced Förster resonant energy transfer (FRET) between quantum dots near a metal nanoshell. It is shown that this process is very efficient near high-aspect-ratio nanoshells. We have also obtained a general expression for the force exerted by an electromagnetic field on an extended polarizable object. This expression is applicable to a wide range of situations important for nanotechnology. Most importantly, this result is of fundamental importance for processes involving interaction of nanoplasmonic fields with metal electrons. Using the obtained expression for the force, we have described a giant surface-plasmoninduced drag-effect rectification (SPIDER), which exists under conditions of the extreme nanoplasmonic confinement. Under realistic conditions in nanowires, this giant SPIDER generates rectified THz potential differences up to 10 V and extremely strong electric fields up to 10^5-10^6 V/cm. It can serve as a powerful nanoscale source of THz radiation. The giant SPIDER opens up a new field of ultraintense THz nanooptics with wide potential applications in nanotechnology and nanoscience, including microelectronics, nanoplasmonics, and biomedicine. Additionally, the SPIDER is an ultrafast effect whose bandwidth for nanometric wires is 20 THz, which allows for detection of femtosecond pulses on the nanoscale.

The theme of my thesis is to investigate the diffraction behavior of subwavelength holes in metal films, and to understand the surface plasmons' (SPs) role in aperture far-field diffraction. We have built a home-made goniometer setup with high-level quality. A series of single hole continuously ranging from k*r>>1 to k*r<

In this thesis devices for controlling the flow of surface plasmon polaritons are described. Dielectric and metallic nanostructures were designed for this purpose, and characterized by leakage radiation microscopy in real and in reciprocal spaces. Manipulation of surface plasmons by dielectric lenses and gradient index elements is presented, and negative refraction, steering and self-collimation of surface plasmons in one- and two-dimensional plasmonic crystals is demonstrated. The achieved degree of control was applied for routing of nanoparticles by optical forces, as well as for two methods of enhancing the figures of merit of plasmonic refractive index sensors, based on the one hand on Fano resonances natural to leakage radiation microscopy, and on the other hand on anisotropie plasmonic bandstructures.

Les capteurs d'image connaissent un regain d'intérêt grâce à la croissance remarquable du secteur de la communication sans fil, et leurs fonctionnalités tendent à se diversifier. Plus particulièrement, une application récente connue sous le nom de capteur de luminosité ambiante (ALS de l'acronyme anglais) est apparue dans le but de proposer un ajustement intelligent du rétro-éclairage dans les appareils mobiles pourvus d'écrans. Les avancées technologiques ont permis la fabrication de smartphones toujours plus fins, ce qui impose une contrainte importante sur la hauteur des capteurs de lumière. Cette réduction d'épaisseur peut être réalisée grâce à l'utilisation de filtres spectraux innovants, plus fins et entièrement sur puce. Dans cette thèse, nous présentons l'étude et la démonstration de filtres plasmoniques adaptés à une intégration dans des produits ALS commerciaux. Les structures de filtrage les plus performantes sont identifiées avec une importance particulière accordée à la stabilité des filtres par rapport à l'angle d'incidence de la lumière et à son état de polarisation. Des schémas d'intégration compatibles CMOS et respectant les contraintes d'une fabrication à l'échelle du wafer sont proposés. Les résonances de plasmon sont étudiées afin d'atteindre des propriétés optiques optimales et une méthodologie spécifique à partir d'un véritable cahier des charges client a été utilisée pour obtenir des performances ALS optimisées. La robustesse des filtres plasmoniques aux dispersions de procédé est analysée à travers l'identification et la modélisation des imprécisions et des défauts typiques d'une fabrication sur wafer 300 mm. A la lumière de ces travaux, une démonstration expérimentale de filtres ALS plasmoniques est réalisée avec le développement d'une intégration à l'échelle du wafer et avec la caractérisation et l'évaluation des performances des structures fabriquées afin de valider la solution plasmonique. / Image sensors have experienced a renewed interest with the prominent market growth of wireless communication, together with a diversification of functionalities. In particular, a recent application known as Ambient Light Sensing (ALS) has emerged for a smarter screen backlight management of display-based handheld devices. Technological progress has led to the fabrication of thinner handsets, which imposes a severe constraint on light sensors' heights. This thickness reduction can be achieved with the use of an innovative, thinnest and entirely on-chip spectral filter. In this work, we present the investigation and the demonstration of plasmonic filters aimed for commercial ALS products. The most-efficient filtering structures are identified with strong emphasis on the stability with respect to the light angle of incidence and polarization state. Integration schemes are proposed according to CMOS compatibility and wafer-scale fabrication concerns. Plasmon resonances are studied to reach optimal optical properties and a dedicated methodology was used to propose optimized ALS performance based on actual customers' specifications. The robustness of plasmonic filters to process dispersions is addressed through the identification and the simulation of typical 300 mm fabrication inaccuracies and defects. In the light of these studies, an experimental demonstration of ALS plasmonic filters is performed with the development of a wafer-level integration and with the characterization and performance evaluation of the fabricated structures to validate the plasmonic solution.

Ce travail de thèse traite de la production d’hydrogène par le procédé de photoélectrocatalyse en utilisant une photoanode à base de nanotubes de TiO2 verticalement alignés. L’utilisation du TiO2 étant limité pour des applications solaires en raison de son large gap, il est nécessaire de le modifier. Deux approches sont proposées pour modifier les nanotubes de TiO2 et leur permettre d’absorber la lumière visible. La première est une modification chimique du TiO2 par co-dopage cationique-anionique (Ta-N) ou (Nb-N). Les cations sont insérés durant la croissance des nanotubes grâce à une approche inédite, et l’azote est inséré durant le traitement thermique. Ceci a pour effet la formation d’orbitales hybrides qui entraîne une réduction du gap et une activité sous lumière visible, tout en permettant une stabilité de la structure. La seconde approche consiste à déposer des nanoparticules d’Ag sur la surface des nanotubes de TiO2. Grâce au contrôle de la morphologie des nanoparticules d’Ag, leur résonnance plasmonique permet de stimuler l’absorption du TiO2 et ainsi d’augmenter son rendement à la fois sous lumière UV et sous lumière visible. / This work is about the production of hydrogen by photoelectrocatalysis using a vertically aligned TiO2 nanotubes based photoanode. Utilization of TiO2 for solar applications is limited due to its large band gap, it has to be modified. Two approaches are proposed for the modification of the TiO2 nanotubes to make them absorb visible light. The first one is the chemical modification of the TiO2 by (Ta-N) or (Nb-N) cationic-anionic co-doping. Cations are inserted during the growth of the nanotubes by a novel approach, and nitrogen is inserted during heat treatment. This leads to the formation of hybrid orbitals resulting in a band gap reduction and of activity under visible light. The second approach consists of the deposition of Ag nanoparticles on the surface of the TiO2 nanotubes. Thanks to the control of the morphology of the Ag nanoparticles, their plasmonic resonance can enhance the absorption of TiO2 and thus increase its activity both under UV and visible light.

Submitted by Fabio Sobreira Campos da Costa (fabio.sobreira@ufpe.br) on 2017-04-27T13:00:02Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Tese_Euclides_Almeida_Fisica.pdf: 5907240 bytes, checksum: 503a5b57e757a03f24206d4d3d26032c (MD5) / Made available in DSpace on 2017-04-27T13:00:02Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Tese_Euclides_Almeida_Fisica.pdf: 5907240 bytes, checksum: 503a5b57e757a03f24206d4d3d26032c (MD5) Previous issue date: 2012-07-30 / CNPQ / O principal objetivo deste trabalho foi investigar fenômenos ópticos ultrarrápidos em sistemas nanoestruturados empregando diferentes técnicas espectroscópicas não lineares, tanto no domínio do tempo quanto no domínio da frequência. Para fornecer uma base adequada que permita entender os experimentos feitos nessa tese, os princípios físicos das espectroscopias ópticas não lineares são apresentados. Inicialmente é apresentada uma descrição da função resposta não linear no domínio do tempo. A evolução temporal da polarização óptica, que gera o sinal espectroscópico, é descrita em detalhes usando uma teoria de perturbação diagramática. Técnicas ópticas não lineares são apresentadas, tais como eco de fótons, bombeamento-e-sonda e hole burning, assim como o comportamento dinâmico de um material pode ser interpretado a partir do sinal gerado. A técnica de mistura degenerada de quatro ondas com luz incoerente foi usada para investigar, pela primeira vez, o defasamento ultrarrápido de éxcitons em uma vitrocerâmica contendo nanocristais de niobato de sódio. O tempo de defasamento medido (T2 = 20 fs) indica qu empregada para investigar processos de transferência de carga em colóides com nanopartículas de TiO2 e rodamina 6G. O comportamento do sinal de depleção transiente é comparado com o observado para a rodamina livre suspensa em etanol. A análise dos resultados permitiu atribuir o comportamento de depleção à transferência de carga de estados excitados termalizados das moléculas de corante para a banda de condução do semicondutor e a transferência no sentido inverso do semicondutor para as moléculas. / The main objective of this work was the investigation of ultrafast optical phenomena in selected nanostructured systems employing different nonlinear spectroscopic techniques, either in the time or the frequency domain. To provide an appropriate background to understand the performed experiments the principles of nonlinear optical spectroscopies are presented. Initially a description of the nonlinear optical response function in the time domain is given. The time evolution of the optical polarization, that gives rise to the spectroscopic signal, is described in detail using a diagrammatic perturbation theory. Nonlinear optical techniques are discussed such as photon echoes, pump-and-probe and hole-burning, as well as how the dynamical behavior of a material can be interpreted from the generated signals. The degenerate four-wave mixing technique with incoherent light was used to investigate for the first time the ultrafast dephasing of excitons in a glass-ceramic containing sodium niobate nanocrystals. The short dephasing time measured (T2 = 20 fs) indicates that different dephasing channels contribute for the excitonic dephasing, namely: electron-electron scattering, electron-phonon coupling and fast trapping of electrons in defects on the nanocrystals interface. Low-temperature luminescence experiments were also performed to measure excitonic and trap states lifetimes. The persistent spectral holeburning technique was applied to measure localized surface plasmons dephasing times in colloidal silver nanoparticles capped with different stabilizing molecules. The dependence of T2 with three different stabilizers was demonstrated and theoretically analyzed. The results show that the dephasing times are shorter than the theoretically calculated T2 using the bulk dielectric functions of the metal. This discrepancy is attributed to changes in the electronic density of states at the nanoparticles interface caused by the presence of the stabilizers. Ab-initio calculations based on the Density Functional Theory were performed to further understand the interaction between the nanoparticles and stabilizing agents. The femtosecond transient absorption technique was employed to study the ultrafast dynamics of in-gap states in a glassceramics containing sodium niobate nanocrystals. Two main temporal components were found for the excited state absorption signal: a fast component, with decay time of ≈ 1 ps, and a slower component which is attributed to deep trap states. This slower component is responsible for the excited state absorption contribution in optical limiting experiments previously reported in the literature. The dynamics of the optical limiting in this sample was also studied, in the millisecond range, exciting the sample with a train of femtosecond pulses. The optical limiting behavior reflects the dynamics of population in the excited and trap states and this dynamics was modeled using rate equations for the electronic states’ populations. Finally, the pump-andprobe transient absorption technique was employed to investigate charge-transfer processes in colloids with rhodamine 6G and TiO2 nanoparticles. The transient bleaching signal behavior is compared with the one observed for unlinked rhodamine 6G dissolved in ethanol. The analysis of the results allowed the attribution of the bleaching behavior to charge-transfer from thermalized excited states of the dye molecules to the semiconductor conduction band and to the back charge-transfer from the semiconductor to the molecules.