The high speed transfer of information in materials with dimensions below the sub-diffraction limit is essential for future technological developments. Metallic nanoparticle (NP) waveguides serve a unique role in efficient energy transfer in this size regime. Light may be confined to metallic structures and propagate along the surface of the waveguide via propagating plasmon waves known as surface plasmon polaritons (SPPs). Plasmon propagation of energy in metallic structures is not perfect however and damping losses from the waveguide material lead to a characteristic exponential decay in the plasmon near field intensity. This decay length is known as the propagation length and serves as an excellent metric to compare various waveguide materials and structures to one another at particular excitation wavelengths. This thesis presents recent work in the development of a novel measurement technique termed bleach imaged plasmon propagation (BlIPP). BlIPP uses the photobleaching property of fluorophores and far field fluorescence microscopy to probe the near-field intensity of propagating plasmons and determine the propagation length. The experimental setup, image analysis, conditions, and application of BlIPP are developed within this thesis and an in depth review of the 1-photon photobleaching mechanism is also investigated. The BlIPP method is used to investigate long plasmon propagation lengths along straight chains of tightly packed Au NPs through the coupling of light to sub-radiant propagating modes, where radiative energy losses are suppressed. The findings of this work reveal, experimentally, the importance of small gap distances for the propagation of energy. Complex chain architectures are then explored using BlIPP measurements of tightly packed straight and bent chains of spherical silver NPs. We observe the highly efficient propagation of energy around sharp corners with no additional bending losses. The findings of this thesis demonstrate the advantages and capabilities of using BlIPP propagation length measurement. Further, BlIPP is used to reveal the advantage of coupling light to sub-radiant modes of NP chains, which demonstrate the ability to guide light efficiently across long distances and around complex structures, bringing us a step closer to the goal of applying plasmonic devices and circuitry in ultra compact opto-electronic devices.

Thermophotovoltaic (TPV) devices, also known as (nano-TPVs) are energy-conversion systems which generate electric current from thermal radiation energy by a heat source. Although their conversion efficiency is limited in the far field by the Schockley-Queisser limit, in near field the heat flux transferred to a TPV cell can be significantly enchanced due to the contribution of evanescent waves, in particular supporting a surface mode. Unfortunately, spectral mismatch between the emitter and the TPV cell spectrum limits the TPV conversion efficiency. Photons with energy lower than the TPV cell bandgap may not be able to create electron-hole pairs because mobile carriers start diffusing and drifting between conductance and valence band, and try to exceed the upper limit of the band. This destroys the thermal equilibrium of the semiconductor and results in excess heat. Also, for high energy photons, the difference between the photon's energy and the bandgap energy is lost in Joule heating. Thus, quasimonochromatic, narrow-band and coherent emitters at a frequency near the energy bandgap of the converter is an ideal source to achieve high conversion efficiency. Nano-TPV device consisting of tungsten thermal emitter, maintained at 1200K, and the cell made of GaInAsSb are considered; thermal management system is reviewed assuming a constant heat flux boundary due to heat generation by the cell with a fluid temperature fixed at 293K. Tungsten thermal selective emitters are designed, characterized and optimized based on two-dimensional (2D) tungsten PhC by controlling periodic triangular grooves such that channel plasmon polaritons (CPPs) are coupled efficiently into these grooves to excite a localized groove modes which are well-matched to the GaInAsSb cell external quantum efficiency (EQE). The results show that power output and the 2D TE normal efficiency of the system are predicted to be 0.82x10⁴ W/m² and 43.8%, respectively. This leads to a promising device for many different sectors such as military, space and semiconductor industry. / text

With the manufacture of nano-scale features in the last ten years, it is possible to do optical experiments on features as small as a tenth/hundredth wavelength. It turns out that the experimental data cannot be explained by classical diffraction theories. Thus, it is necessary to develop new methods or use existing approaches which are effective in other fields, to solve problems in photonics. We use finite difference time domain (FDTD), to study transmission properties of sub-wavelength slits in a metallic film. By doing simulations on periodic and single slits, we confirm that the TE mode has a cutoff while a TM mode always has a propagating mode in the small apertures. Then we find that the transmittance is minimum when the array period is equal to the wavelength of surface plasmon polariton (SPP) at normal incidence. In fact, the SPP-like waves exist in both periodic and isolated slits, and they help the transmittance of small apertures. In order to establish the role of SPP in the transmission mechanism, it is necessary to single out each mode from the total fields. We developed Bloch mode method (BMM) to calculate the amplitudes of the lowest N orders, and the amplitudes tell us which one is dominant (not including the guided mode) at high and low transmission. BMM converges very fast and it is more accurate than FDTD since it does not suffer from numerical dispersion. Both methods can resolve the Wood anomaly and SPP anomaly; however, FDTD converges very slowly at the SPP resonance and oscillates around the value obtained through BMM at the Wood anomaly. BMM is not sensitive to material types, incident angles, and anomalies; it will be a useful tool to investigate similar problems.

Long-range surface plasmon-polaritons are transverse-magnetic polarized optical surface waves formed through the interaction of photons with free electrons at the surface of metal slabs or stripes. They play important roles in a variety of field such as integrated optics, amplifiers and lasers, optical sensing, modulation, etc. Due to their longer propagation length and deeper penetration depth compared to those of single-interface surface plasmon-polaritons, they have become increasingly promising in optical sensing. In sensing applications, it is necessary to reduce the noise level in order to obtain a lower detection limit. One way to achieve this is to use dual- or triple-output Mach-Zehnder interferometers so that the common perturbations among the outputs can be suppressed. The objective of this thesis is to provide deeper insights on the performances of dual- and triple-output Mach-Zehnder interferometers in thermo-optic and optical bulk sensing applications, theoretically and experimentally, and to demonstrate their ability to suppress common perturbations and lower the detection limit. On the theoretical side, the objective is approached by constructing a model for the transfer characteristic. For dual-output Mach-Zehnder interferometers, the plane-wave model is used to develop a general model for thermo-optic sensing and an unbalanced model for optical bulk sensing. For triple-output ones, local normal mode theory is used with modal analysis for the 3×3 coupler portion of the structure. Quantitative methods to analyze and compare different detection schemes are developed. The minimum detectable phase shift is determined for the case of thermo-optic sensing while the detection limit is determined for optical bulk sensing. On the experimental side, the objective is approached by providing a direct experimental demonstration of the transfer characteristics at an optimized operating wavelength for the coupler portion of the device, then comparing to theory. Time traces are carried out and various detection schemes are applied to suppress common perturbations among the outputs, and to improve the minimum detectable phase shift or the detection limit.

An infrared radiometry setup has been developed based on a commercially available FTIR spectrometer for measuring mid-infrared thermal radiation. The setup was calibrated with a lab-built blackbody source. The setup was tested with a grating structure with 4-micron periodicity. Periodic microstructures using nickel and gold are fabricated on elastomeric substrates by use of strain-induced buckling of the nickel layer. The intrinsically low emissivity of gold in the mid-infrared regime is selectively enhanced by the surface plasmonic resonance at three different mid-infrared wavelengths, 4.5 µm, 6.3 µm, and 9.4 µm. As the thermal emission enhancement effect exists only for the polarization perpendicular to the orientation of the microstructures, substantially polarized thermal emission with an extinction ratio of close to 3 is demonstrated. Moreover, the elastically deformed plasmonic thermal emitters demonstrate strain-dependent emission peaks, which can be applied for future mechano-thermal sensing and dynamic thermal signature modulation.

No description available.

Diese Arbeit leistet einen Beitrag zum Verständnis optischer Anregungen in metallischen Nanostrukturen. Am Beispiel ausgewählter Strukturen werden experimentell die Dynamik dieser Anregungen mit Femtosekunden-Zeitauflösung und ihre elektromagnetischen Moden auf der Nanometer-Längenskala untersucht. Anhand winkel- und zeitaufgelöster Transmissionsexperimente an metallischen Dünnfilmgittern wird gezeigt, dass resonante Oberflächenplasmon-Polaritonen (OPPen) wesentlich die optischen Eigenschaften dieser Strukturen beeinflussen. Die Lebensdauer solcher Anregungen wird ermittelt und damit nachgewiesen, dass Kopplungen zwischen OPP-Resonanzen drastische Lebensdauer-Modifikationen zur Folge haben. In einem eigens konstruierten, spektral auflösenden optischen Nahfeldmikroskop werden die elektromagnetischen Feldverteilungen der OPPen direkt abgebildet. Derartige Experimente erlauben erstmals eine Zuordnung der räumlichen Moden zur zeitlichen Dynamik verschiedener OPP-Resonanzen. Diese Erkenntnisse ermöglichen zudem eine Interpretation des nahfeldmikroskopischen Bildkontrasts bezüglich der Beiträge verschiedener vektorieller Komponenten des optischen Nahfeldes. Die selektive Abbildung unterschiedlicher elektrischer und magnetischer Feldkomponenten in Abhängigkeit vom Sondentyp wird demonstriert. Darüberhinaus wird die OPP-Erzeugung in einem Gitter auf dem Schaft einer Nahfeldspitze ausgenutzt, um propagierende OPPen im Apex zu konzentrieren. Ein weiterer Teil der Arbeit nutzt elektrische Feldüberhöhungen an scharfen Metallspitzen für die lokalisierte Erzeugung nichtlinearer optischer Signale. Die Beobachtung intensiver Multiphoton-Elektronenemission nach Femtosekundenanregung stellt ein zentrales Ergebnis dar. Dieser Prozess wird umfangreich charakterisiert und findet seine erste Anwendung in einer neuartigen Rastersondentechnik, in der die örtlich variierende Elektronenemission der Bildgebung dient. / This thesis contributes to the understanding of optical excitations in metallic nanostructures. In experiments on selected model structures, the dynamics of these excitations and their electromagnetic spatial modes are investigated with femtosecond temporal and nanometer spatial resolution, respectively. Angle- and time-resolved transmission experiments on metallic thin film gratings demonstrate the dominant role resonant surface plasmon polaritons (SPPs) play in the optical properties of such structures. The lifetimes of these excitations are determined, and it is shown that coherent couplings among SPP-resonances result in drastic lifetime modifications. The spatial SPP mode profiles are imaged using a custom-built near-field optical microscope. The experiments reveal a direct correlation between the spatial mode structure and the dynamics of different SPP resonances. These findings allow for an interpretation of the near-field optical image contrast in terms of the contributions of different vectorial components of the electromagnetic near-field. A selective imaging of different electric and magnetic field components is demonstrated for various types of near-field probes. Furthermore, the excitation of SPPs in periodic structures is employed in a novel type of near-field tip. The resonant excitation of SPPs in a nanofabricated grating on the shaft of a sharp metallic tip results in their concentration at the tip apex. The final part of the thesis highlights the importance of optical field enhancements for the local generation of nonlinear optical signals at the apex of sharp metallic tips. Specifically, the observation of intense multiphoton electron emission after femtosecond excitation is a major result. This process is thoroughly characterized, and a novel scanning microscopy application based on this effect is presented. In this technique, an image contrast with nanometer resolution arises from spatially varying electron emission rates.

O confinamento da luz em escala nanométrica, em especial para estruturas metálicas, é conferido graças à ação coletiva dos elétrons livres desses materiais que ao entrarem em ressonância com a frequência da radiação incidente geram campos intensos o suficiente para permitir que uma parcela da luz atravesse as cavidades que formam as estruturas, desafiando os limites clássicos da óptica impostos pela teoria escalar da difração. Designa-se a tal ação coletiva dos elétrons na literatura como plasmons polaritons de superfície, ou SPP da sigla em inglês para Surface Plasmon Polariton, conceito há muito estudado em Física do Estado Sólido. Porém, somente a algumas décadas com o domínio sobre a fabricação de estruturas em escala nanométrica, tornou-se possível a análise experimental e a contribuição de SPP na observação de fenômenos em nano-óptica. A ressonância de plasmons em nanoestruturas confere considerável sensibilidade ao índice de refração dos meios próximos a elas, o que abre mais um canal para estudos no campo da interação entre radiação-matéria. Dentre eles há interação de plasmons com íons de terras-raras (ITR). Estes últimos por apresentarem bandas de absorção estreitas e bem definidas, são excelentes opções como elementos na análise da interação destes com os SPPs gerados nas nanoestruturas. Uma maneira de estabelecer o contato direto entre o campo plasmônico e os ITRs é incorpora-los ao substrato no qual o filme metálico onde as nanoestruturas são fabricadas é depositado. Vidros óxidos à base de Telúrio e Germânio reúnem condições favoráveis para esse propósito, por terem alta solubilidade às terras-raras, janela de transparência relativamente larga (0,4 - 5μm) podendo ser analisados desde o visível até o infravermelho e baixa energia de fônon. O presente trabalho consistiu no esforço de criar uma plataforma para estudo direto de interações SPP com o ITR a partir da nano fabricação via técnica de feixe de íons e medir a luz emitida por processo de conversão ascendente do Érbio diretamente pela nanoestrutura devido ao decaimento do íon em SPP e na consequente remissão através da transmissão óptica extraordinária (TOE). A partir de tais medidas há fortes evidências de que a radiação emitida pelo Érbio apresenta a mesma polarização do campo plasmônico originado nas nanoestruturas. / The confinement of light at the nanoscale, especially for metallic structures is achieved due the collective action of free electrons from the material that resonate with the frequency of the incident radiation, generating enhanced fields enough to allow a portion of the light to cross the cavities that form such structures, challenging the classical limits of optics imposed by the scalar diffraction theory. Such collective action of the electrons is known in the literature as surface plasmon polariton (SPP), a concept which has already been studied in Solid State Physics, but only a few decades ago, with the development of fabrication of nanoscale structures has enabled the experimental analysis and the contribution due SPP on the observation of nanoptics phenomena. The plasmon resonance from nanostructures offers considerable sensitivity to the refractive index from the media that surround them, which opens another topic in matter-radiation interaction. There are interactions of plasmons with rare earth ions (REI). The latter class of emitters, presents narrow and well-defined absorption bands, which make them excellent options as probes to the analysis of interaction with the SPPs generated in the nanostructures. To establish direct contact between the plasmonic field and the REIs consists in embedding them into the substrate for the metallic thin film where the structures are assembled. Tellurium and Germanium oxide based glasses gather the conditions for this purpose, because they present high solubility to rare earths, a relatively wide transparency window (0.4 - 5 μm), which enables spectral analysis from visible to infrared, and low phonon energy. The present work consisted in the effort to create a direct platform to study the SPP interactions with the REI from the milling of the samples by ion beam technique; to measure the light emitted from the Erbium\'s upconversion process directly through the nanostructure due the ion decay to SPP and in the consequent remission by extraordinary optical transmission (EOT). From such measurements there are strong evidences that the radiation emitted by Erbium ions presents the same polarization from the plasmonic field originated in nanostructures.

O confinamento da luz em escala nanométrica, em especial para estruturas metálicas, é conferido graças à ação coletiva dos elétrons livres desses materiais que ao entrarem em ressonância com a frequência da radiação incidente geram campos intensos o suficiente para permitir que uma parcela da luz atravesse as cavidades que formam as estruturas, desafiando os limites clássicos da óptica impostos pela teoria escalar da difração. Designa-se a tal ação coletiva dos elétrons na literatura como plasmons polaritons de superfície, ou SPP da sigla em inglês para Surface Plasmon Polariton, conceito há muito estudado em Física do Estado Sólido. Porém, somente a algumas décadas com o domínio sobre a fabricação de estruturas em escala nanométrica, tornou-se possível a análise experimental e a contribuição de SPP na observação de fenômenos em nano-óptica. A ressonância de plasmons em nanoestruturas confere considerável sensibilidade ao índice de refração dos meios próximos a elas, o que abre mais um canal para estudos no campo da interação entre radiação-matéria. Dentre eles há interação de plasmons com íons de terras-raras (ITR). Estes últimos por apresentarem bandas de absorção estreitas e bem definidas, são excelentes opções como elementos na análise da interação destes com os SPPs gerados nas nanoestruturas. Uma maneira de estabelecer o contato direto entre o campo plasmônico e os ITRs é incorpora-los ao substrato no qual o filme metálico onde as nanoestruturas são fabricadas é depositado. Vidros óxidos à base de Telúrio e Germânio reúnem condições favoráveis para esse propósito, por terem alta solubilidade às terras-raras, janela de transparência relativamente larga (0,4 - 5μm) podendo ser analisados desde o visível até o infravermelho e baixa energia de fônon. O presente trabalho consistiu no esforço de criar uma plataforma para estudo direto de interações SPP com o ITR a partir da nano fabricação via técnica de feixe de íons e medir a luz emitida por processo de conversão ascendente do Érbio diretamente pela nanoestrutura devido ao decaimento do íon em SPP e na consequente remissão através da transmissão óptica extraordinária (TOE). A partir de tais medidas há fortes evidências de que a radiação emitida pelo Érbio apresenta a mesma polarização do campo plasmônico originado nas nanoestruturas. / The confinement of light at the nanoscale, especially for metallic structures is achieved due the collective action of free electrons from the material that resonate with the frequency of the incident radiation, generating enhanced fields enough to allow a portion of the light to cross the cavities that form such structures, challenging the classical limits of optics imposed by the scalar diffraction theory. Such collective action of the electrons is known in the literature as surface plasmon polariton (SPP), a concept which has already been studied in Solid State Physics, but only a few decades ago, with the development of fabrication of nanoscale structures has enabled the experimental analysis and the contribution due SPP on the observation of nanoptics phenomena. The plasmon resonance from nanostructures offers considerable sensitivity to the refractive index from the media that surround them, which opens another topic in matter-radiation interaction. There are interactions of plasmons with rare earth ions (REI). The latter class of emitters, presents narrow and well-defined absorption bands, which make them excellent options as probes to the analysis of interaction with the SPPs generated in the nanostructures. To establish direct contact between the plasmonic field and the REIs consists in embedding them into the substrate for the metallic thin film where the structures are assembled. Tellurium and Germanium oxide based glasses gather the conditions for this purpose, because they present high solubility to rare earths, a relatively wide transparency window (0.4 - 5 μm), which enables spectral analysis from visible to infrared, and low phonon energy. The present work consisted in the effort to create a direct platform to study the SPP interactions with the REI from the milling of the samples by ion beam technique; to measure the light emitted from the Erbium\'s upconversion process directly through the nanostructure due the ion decay to SPP and in the consequent remission by extraordinary optical transmission (EOT). From such measurements there are strong evidences that the radiation emitted by Erbium ions presents the same polarization from the plasmonic field originated in nanostructures.

Dans cette thèse, nous étudions les propriétés optiques d'un système multicouche (air-Au-SiO₂-Au-Ti-verre). Les interfaces sont planes et la modélisation est réalisée en utilisant les coefficients de Fresnel à l'interface et la propagation d'ondes planes dans les couches. Deux modèles sont utilisés où l'échantillon est : i) excité par une source à l'infini ; ii) excité par une source locale. Dans l'expérience que nous avons modélisée l'empilement est excité par les électrons tunnel inélastiques dans un microscope à effet tunnel (STM). Dans le modèle, le courant tunnel inélastique est remplacé par un dipôle oscillant vertical. En utilisant ces modèles, nous avons calculé les flux réfléchis (reflectance) et transmis (transmittance) d'une source de lumière à l'infini et le flux transmis de l'excitation locale. La reflectance, transmittance et le flux transmis montrent des modes plasmoniques (surface plasmon polaritons (SPP)) et photoniques (guide d'onde (WG)). A des longueurs d'onde particulières, les courbes de dispersion des SPP et WG présentent un croisement évité. Le choix des épaisseurs d'or et de silice a deux contraintes: une amplitude importante des observables et une large dépendance en longueurs d'onde du vecteur d'onde dans le plan. Nous étudions aussi l'influence des épaisseurs sur les observables. Nous avons trouvé que les observables ont des amplitudes importantes à pour une épaisseur d'or de [10, 90 nm] pour l'empilement de trois couches et de [10, 50 nm] pour celui de six couches. Les modes de guide d'onde apparaissent pour une épaisseur de la couche de silice de >190 nm. Afin de caractériser la localisation du champ dans l'empilement et déterminer la nature du mode, nous avons calculé le champ électrique en fonction de la coordonnée de pénétration z. Nous avons trouvé que pour le mode SPP le champ est localisé à l'interface Au-air, tandis que le champ électrique du guide d'onde est confiné dans la couche de silice. Les résultats théoriques présentés sont en bon accord avec les résultats des études expérimentales menées dans notre groupe. / In this thesis, we investigate the optical properties of a six-layer stack (air-Au-SiO₂-Au-Ti-glass). The interfaces are flat and the modeling is performed using elementary Fresnel expressions at the interface and plane wave propagation in the layers. Two models are used where the sample is: i) excited by a source at infinity (excitation by source at infinity (ESI)); ii) excited by a local source. In the experiments we are modeling this source consists of the inelastic tunneling electrons from a scanning tunneling microscope (STM). In our modeling this source is replaced by a vertical oscillating dipole. Using these two models one calculates the reflected (reflectance) and the transmitted (transmittance) flux from a source at infinity and the transmitted flux of a local source. Surface plasmon polariton (SPP) and wave guide (WG) modes may be identified in the reflectance, transmittance and transmitted flux. In a particular wavelength domain the SPP and WG repel each other giving rise to an avoided crossing. The choice of the gold (Au) and silica (SiO₂) thicknesses of the six-layer stack is guided by two requirements: high amplitude of the observable and wide wavelength dependence of the in-plane wave vector. We also study the influence of the gold and silica thicknesses on the observables. We find that the observables are significant for dAu[10, 90 nm] for the three and dAu[10, 50 nm] for six layer stacks and this predictive study guided the choice of the experimental sample thicknesses. The wave guide mode appears for dSiO₂ >190 nm. The electric field as a function of the penetration coordinate z is calculated in order to characterize the location of the field in the stack and to assign the nature of the modes. We observe that for the SPP the electric field is confined at the Au-air interface whereas, the electric fields corresponding to the WG mode are confined inside SiO₂ layer. Our calculations presented in this work are in good agreement with the experimental measurements performed in our group.