Surface plasmon-polaritons are optical surface waves formed through the interaction of photons with free electrons at the surface of metals. They offer interesting applications in a broad range of scientific fields such as physics, chemistry, biology, and material science. However, many of such applications face limitations imposed by the high propagation losses of these waves at visible and near-infrared wavelengths, which result mainly from power dissipation in the metal. In principle, the propagation losses of surface plasmon-polaritons can be compensated through optical amplification. The objective of this thesis is to provide deeper insights on the physics of surface plasmon-polariton amplification and spontaneous emission in surface plasmon-polariton amplifiers through theoretical and experimental vehicles applied (but not necessarily restricted) to a particular plasmonic mode termed long-range surface plasmon-polariton. On the theoretical side, the objective is approached by developing a realistic theoretical model to describe the small-signal amplification of surface plasmon-polaritons in planar structures incorporating dipolar gain media such as organic dye molecules, rare-earth ions, and quantum dots. This model takes into account the inhomogeneous gain distribution formed near the metal surface due to a non-uniform excitation of dipoles and due to a position-dependent excited-state dipole lifetime that results from near-field interactions between the excited dipoles and the metal. Also, a theoretical model to describe the amplified spontaneous emission of surface plasmon-polaritons supported by planar metallic structures is developed. This model takes into account the different energy decay channels into which an exited dipole located in the vicinity of the metal can relax. The validity of this model is confirmed through experimentation. On the experimental side, the objective is approached by providing a direct experimental demonstration of complete loss compensation in a plasmonic waveguide. The experiments are conducted using the long-range surface plasmon-polariton supported by a symmetric thin gold waveguide incorporating optically pumped organic dye molecules in solution as the gain medium. Also, an experimental study of spontaneous emission in a long-range surface plasmon-polariton amplifier is presented. It is shown that this amplifier benefits from a low spontaneous emission into the amplified mode, which leads to an optical amplifier with low noise characteristics. The experimental setup and techniques are explained in detail.

abstract: The study of subwavelength behavior of light and nanoscale lasing has broad potential applications in various forms of computation i.e. optical and quantum, as well as in energy engineering. Although this field has been under active research, there has been little work done on describing the behaviors of threshold and saturation. Particularly, how the gain-molecule behavior affects the lasing behavior has yet to be investigated. In this work, the interaction of surface-plasmon-polaritons (SPPs) and molecules is observed in lasing. Various phenomenologies are observed related to the appearance of the threshold and saturation regions. The lasing profile, as a visual delimiter of lasing threshold and saturation, is introduced and used to study various parametrical dependencies of lasing, including the number-density of molecules, the molecular thickness and the frequency detuning between the molecular transition frequency and the SPP resonant frequency. The molecular population distributions are studied in terminal and dynamical methods and are found to contain unexpected and theoretically challenging properties. Using an average dynamical analysis, the simulated spontaneous emission cascade can be clearly seen. Finally, theoretical derivations of simple 1D strands of dipoles are presented in both the exact and mean-field approximation, within the density matrix formalism. Some preliminary findings are presented, detailing the observed behaviors of some simple systems. / Dissertation/Thesis / Masters Thesis Chemical Engineering 2017

Made available in DSpace on 2014-12-17T15:14:58Z (GMT). No. of bitstreams: 1 ManoelSV_TESE_capa_ate_pag67.pdf: 3395617 bytes, checksum: 7b8445696b35d33ae99c6f6fe1c1b75d (MD5) Previous issue date: 1999-07-12 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Neste trabalho investigamos as propriedades dos espectros de polariton de plasmons e de ondas de luz em super-redes semicondutoras e em multicamadas diel?tricas, respectivamente, arranjadas em um padr?o quasi-peri?dico. Esta quasi-periodicidade pode ser do tipo das chamadas sequ?ncias substitucionais. Elas s?o caracterizadas pela natureza de seus espectros de Fourier, que pode ser do tipo dense pur? point (sequ?ncia de Fibonacci), singular continuous (sequ?ncias de Thue-Morse e duplo-per?odo) e absolutely continuous ( sequ?ncia de Rudin-Shapiro). Com o objetivo de estudar o espectro de polariton de plasmon, usamos um conveniente modelo te?rico baseado no tratamento da matriz-transfer?ncia, com as camadas caracterizadas por uma fun??o diel?trica dependente da frequ?ncia, incluindo efeitos de retardamento. Encontramos um espectro fractal caracterizado por uma lei de pot?ncia para a distribui??o de bandas em cada tipo de estrutura quasi-peri?dica. Para a propaga??o das ondas de luz em multicamadas diel?tricas, os coeficientes de transmiss?o s?o derivados atrav?s da determina??o da matriz-transfer?ncia ?ptica. Uma compara??o entre a incid?ncia obl?qua e a incid?ncia normal, nos mostra comportamentos bastante diferentes do espectro de transmit?ncia para um intervalo particular de frequ?ncia. No caso da incid?ncia normal, apresentamos resultados num?ricos que ilustram o aspecto auto-similar destes espectros, assim como mostram suas impress?es digitais ?pticas que s?o determinadas atrav?s dos mapas de retorno de seus coeficientes de transmiss?o. Finalmente, investigamos tamb?m as propriedades multifractais destes espectros (polariton de plasmons e ondes de luz)

Made available in DSpace on 2014-12-17T15:14:59Z (GMT). No. of bitstreams: 1 CarlosAAA_TESE.pdf: 1802680 bytes, checksum: 89f89876081eff2b7412d1b633210e6c (MD5) Previous issue date: 2012-03-03 / In this work, we present a theoretical study of the propagation of electromagnetic waves in multilayer structures called Photonic Crystals. For this purpose, we investigate the phonon-polariton band gaps in periodic and quasi-periodic (Fibonacci-type) multilayers made up of both positive and negative refractive index materials in the terahertz (THz) region. The behavior of the polaritonic band gaps as a function of the multilayer period is investigated systematically. We use a theoretical model based on the formalism of transfer matrix in order to simplify the algebra involved in obtaining the dispersion relation of phonon-polaritons (bulk and surface modes). We also present a quantitative analysis of the results, pointing out the distribution of the allowed polaritonic bandwidths for high Fibonacci generations, which gives good insight about their localization and power laws. We calculate the emittance spectrum of the electromagnetic radiation, in THZ frequency, normally and obliquely incident (s and p polarized modes) on a one-dimensional multilayer structure composed of positive and negative refractive index materials organized periodically and quasi-periodically. We model the negative refractive index material by a effective medium whose electric permittivity is characterized by a phonon-polariton frequency dependent dielectric function, while for the magnetic permeability we have a Drude like frequency-dependent function. Similarity to the one-dimensional photonic crystal, this layered effective medium, called polaritonic Crystals, allow us the control of the electromagnetic propagation, generating regions named polaritonic bandgap. The emittance spectra are determined by means of a well known theoretical model based on Kirchoff s second law, together with a transfer matrix formalism. Our results shows that the omnidirectional band gaps will appear in the THz regime, in a well defined interval, that are independent of polarization in periodic case as well as in quasiperiodic case / Neste trabalho, apresentamos um estudo te?rico da propaga??o das ondas eletromagn?ticas em estruturas de multicamadas denominadas de Cristais Fot?nicos. Para este fim, investigamos os band gaps dos polaritons de fonons em multicamadas peri?dicas e quasi-peri?dica (tipo Fibonacci), compostas por dois materiais com ?ndices de refra??o positivo e negativo na regi?o de terahertz (THZ). O comportamento dos band gaps polarit?nicos como uma fun??o do per?odo da multicamada ? investigado sistematicamente. Utilizamos um modelo te?rico baseado no formalismo da matriz de transfer?ncia com o objetivo de simplificar a ?lgebra envolvida na obten??o da rela??o de dispers?o dos polaritons de fonons (modos de volume e superf?cie). Tamb?m, apresentamos uma an?lise quantitativa dos resultados, apontando para a distribui??o das larguras das bandas polarit?nicas permitidas para altas gera??es de Fibonacci, que nos d? uma boa compreens?o sobre sua localiza??o e leis de pot?ncia. Calculamos o espectro de emit?ncia da radia??o eletromagn?tica, na frequ?ncia de THz, incidente normalmente e obliquamente (modos polarizados s e p) sobre uma estrutura unidimensional de multicamadas composta por materiais com ?ndices de refra??o positivo e negativo organizados periodicamente e quasi-periodicamente. Modelamos o material com ?ndice de refra??o negativo por um meio efetivo cuja permissividade ? caracterizada por uma fun??o diel?trica dependente da frequ?ncia do polariton de fonon, enquanto para a permeabilidade magn?tica temos uma fun??o tipo Drude dependente da frequ?ncia. Semelhante ao cristal fot?nico unidimensional, este meio efetivo em camadas, chamado cristal polarit?nico, nos permite o controle da propaga??o electromagn?tica, gerando regi?es denominadas de bang gaps polarit?nicos. Os espectros de emit?ncia s?o determinados por meio de um modelo te?rico bem conhecido baseado na segunda lei de Kirchoff, juntamente com o formalismo da matriz de transfer?ncia. Nossos resultados mostram que aparecem bang gaps ominidirecionais no regime de THz, num intervalo bem definido, que s?o independentes da polariza??o no caso peri?dico bem como no caso quasi-peri?dico

Over the past few years, surface plasmon photodetectors have been of renewed interest. This is due to their unique double functionality of combining an SPP waveguide structure with a photodetection structure. This thesis investigates the performance of a Schottky nano-photodetector integrated into a finite width metal stripe which is covered by air on top and supported by silicon at the bottom, supporting the propagation of bound SPP modes. Properties of surface plasmons, including the sub-wavelength confinement, were exploited to increase the efficiency of the detector. The detector performance was explored via applying end-fire coupling to the fundamental supported mode, then the results were used to calculate the devices responsivity, dark current, minimum detectable power, and photocurrent for various metal lengths. End fire coupling to a Schottky mode supported by a nano-structured metal was done for what is believed to be the first time.

Different types of plasmonic nanostructures are proposed and examined experimentally and theoretically, with a view towards sensing applications. First, a self-assembly approach was developed to create arrays of well-ordered glass-supported gold nanoparticles (AuNPs) with controllable particle size and inter-particle spacing. Then, a periodic array of gold nano-disks (AuNDs) supported by a Bragg reflector was proposed and examined in a search for Fano resonances in its optical response. Arrays of heptamer-arranged nanoholes (HNH) in a thin gold film were also proposed and explored theoretically and experimentally, revealing a very rich spectrum of resonances, several exhibiting a Fano lineshape. A commercial implementation of the vectorial finite element method (FEM) was used to model our plasmonic structures. Taking advantage of the periodic nature of the structures, a unit cell containing a single element was modelled. The transmittance, reflectance or absorbance spectra were computed, and the associated electromagnetic fields were obtained by solving the vector wave equations for the electromagnetic field vectors throughout the structures, subject to the applicable boundary conditions, and the applied source fields. The sensing performance of the structures, based on the bulk sensitivity, surface sensitivity and figure of merit (FOM) was calculated. First, a novel bottom-up fabrication approach was applied (by our collaborators) to form a periodic array of AuNPs with controllable size over large areas on SiO2 substrates. In this method, self-assembly of block copolymer micelles loaded with metal precursors was combined with a seeding growth route to create ordered AuNPs of desired size. It was shown that this new fabrication method offers a new approach to tune the AuNP size and edge-to-edge inter-particle spacing while preserving the AuNP ordering. The optical characteristics of the AuNP arrays, such as their size, interparticle spacing, localized surface plasmon resonance (LSPR) wavelength, and bulk sensitivity, were examined, numerically and experimentally. This proposed novel fabrication method is applicable for low-cost mass-production of large-area arrays of high-quality AuNPs on a substrate for sensing applications. Then, we proposed and examined the formation of Fano resonances in a plasmonic-dielectric system consisting of uncoupled gold nano-disk (AuND) arrays on a quarter-wave dielectric stack. The mechanism behind the creation of Fano resonances was explained based on the coherent interference between the reflection of the Bragg stack and the LSPPs of the AuNDs. Fano parameters were obtained by fitting the computational data to the Fano formula. The bulk sensitivities and figure of merit of the Fano resonances were calculated. This plasmonic structure supports Fano resonances with a linewidth around 9 nm which is much narrower than the individual AuND LSPP bandwidth ( 80 nm) and the Bragg stack bandwidth ( 100 nm). Supporting Fano resonances with such a narrow linewidth, the structure has a great potential to be used for sensing applications. Also, this metallic-dielectric nanostructure requires no near-field coupling between AuNDs to generate the Fano resonances. So, the AuNDs can be located far enough from each other to simplify the potential fabrication process. The optical properties of HNH arrays on an SiO2 substrate were investigated, numerically and experimentally. Helium focused ion beam (HeFIB) milling was applied (by Dr. Choloong Hahn) to fabricate well-ordered and well-defined arrays of HNHs. Transmittance spectra of the structures were obtained as the optical response, which exhibits several Fano resonances. Then, the mechanism behind the formation of the Fano resonances was explained, and the sensing performance of the structure was inspected by measuring the bulk sensitivities. This array of nanohole cluster is exciting because it supports propagating SPPs and LSPPs, and also Wood’s anomaly waves, which makes the optical response very rich in excitations and spectral features. Also, as a periodic array of sub-wavelength metallic nanoholes, the system produces extraordinary optical transmission - highly enhanced transmission through (otherwise) opaque metallic films at specific wavelengths, facilitating measurement acquisition in transmission.

Patterning graphene with a spatially periodic potential provides a powerful means to modify its electronic properties. In particular, in twisted bilayers, coupling to the resulting moiré superlattice yields an isolated flat band that hosts correlated many-body phases. However, both the symmetry and strength of the effective moiré potential are constrained by the constituent crystals, limiting its tunability. Here, we have exploited the technique of dielectric patterning⁶ to subject graphene to a one-dimensional electrostatic superlattice (SL). We observed the emergence of multiple Dirac cones and found evidence that with increasing SL potential the main and satellite Dirac cones are sequentially flattened in the direction parallel to the SL basis vector, behavior resulting from the interaction between the one-dimensional SL electric potential and the massless Dirac fermions hosted by graphene. Our results demonstrate the ability to induce tunable anisotropy in high-mobility two-dimensional materials, a long-desired property for novel electronic and optical applications. Moreover, these findings offer a new approach to engineering flat energy bands where electron interactions can lead to emergent properties. The photon analog of electronic superlattice is photonic crystals. Efficient control of photons is enabled by hybridizing light with matter. The resulting light-matter quasi-particles can be readily programmed by manipulating either their photonic or matter constituents. Here, we hybridized infrared photons with graphene Dirac electrons to form surface plasmon polaritons (SPPs) and uncovered a previously unexplored means to control SPPs in structures with periodically modulated carrier density. In these photonic crystal structures, common SPPs with continuous dispersion are transformed into Bloch polaritons with attendant discrete bands separated by bandgaps. We explored directional Bloch polaritons and steered their propagation by dialing the proper gate voltage. Fourier analysis of the near-field images corroborates that this on-demand nano-optics functionality is rooted in the polaritonic band structure. Our programmable polaritonic platform paves the way for the much-sought benefits of on-the-chip photonic circuits.

In this thesis by articles, I propose and demonstrate the full design, fabrication and characterization of optical biosensors based on (Bloch) Long Range Surface Plasmon Polaritons (LRSPPs). Gold waveguides embedded in CYTOP with an etched microfluidic channel supporting LRSPPs and gold waveguides on a one-dimensional photonic crystal (1DPC) supporting Bloch LRSPPs are exploited for biosensing applications. Straight gold waveguides embedded in CYTOP supporting LRSPPs as a biosensor, are initially used to measure the kinetics constants of protein-protein interactions. The kinetics constants are extracted from binding curves using the integrated rate equation. Linear and non-linear least squares analysis are employed to obtain the kinetics constants and the results are compared. The device is also used to demonstrate enhanced assay formats (sandwich and inhibition assays) and protein concentrations as low as 10 pg/ml in solution are detected with a signal-to-noise ratio of 20 using this new optical biosensor technology. CYTOP which has a refractive index close to water is the fluoropolymer of choice in current state of the art waveguide biosensors. CYTOP has a low glass transition temperature which introduces limitations in fabrication processes. A truncated 1D photonic crystal can replace a low-index polymer cladding such as CYTOP, to support Bloch LRSPPs within the bandgap of the 1DPC over a limited ranges of wavenumber and wavelength. Motivated by quality issues with end facets, we seek to use grating couplers in a broadside coupling scheme where a laser beam emerging from an optical fiber excites Bloch LRSPPs on a Au stripe on a truncated 1D photonic crystal. Adiabatic and non-adiabatic flared stripes accommodating wide gratings size-matched to an incident Gaussian beam are designed and compared to maximise the coupling efficiency to LRSPPs. The gratings are optimized, initially, through 2D modelling using the vectorial finite element method (FEM). Different 3D grating designs were then investigated via 3D modelling using the vectorial finite difference time domain (FDTD) method. Given their compatibility with planar technologies, gratings and waveguides can be integrated into arrays of biosensors enabling multi-channel biosensing. A multi-channel platform can provide, e.g., additional measurements to improve the reliability in a disease detection problem. Thus, a novel optical biosensor based on Bloch LRSPPs on waveguide arrays integrated with electrochemical biosensors is presented. The structures were fabricated on truncated 1D photonic crystals comprised of 15 period stack of alternating layers of SiO2/Ta2O5. The optical biosensors consist of Au stripes supporting Bloch LRSPPs and integrate grating couplers as input/output means. The Au stripes also operate as a working electrode in conjunction with a neighboring Pt counter electrode to form an electrochemical sensor. The structures were fabricated using bilayer lift-off photolithography and the gratings were fabricated using overlaid e-beam lithography. The planar waveguides are integrated into arrays capable of multichannel biosensing. The wafer is covered with CYTOP as the upper cladding with etched microfluidic channels, and wafer-bonded to a borofloat silica wafer to seal the fluidic channels and enable side fluidic interfaces. The proposed device is capable in principle of simultaneous optical and electrochemical sensing and could be used to address disease detection problems using a multimodal strategy.

Nonpolar ZnO/ZnMgO-based optical microcavities have been grown on (10-10) m-plane ZnO substrates by plasma-assisted molecular beam epitaxy. Reflectivity measurements indicate an exponential increase of the cavity quality factor with the number of layers in the distributed Bragg reflectors. Most importantly, microreflectivity spectra recorded with a spot size in the order of 2 lm show a negligible photonic disorder (well below 1 meV), leading to local quality factors equivalent to those obtained by macroreflectivity. The anisotropic character of the nonpolar heterostructures manifests itself both in the surface features, elongated parallel to the in-plane c direction, and in the optical spectra, with two cavity modes being observed at different energies for orthogonal polarizations.

We address the problem of the correct description of light-matter coupling for excitons and cavity photons in the case of systems with multiple photon modes or excitons, respectively. In the literature, two different approaches for the phenomenological coupling Hamiltonian can be found: Either one single Hamiltonian with a basis whose dimension equals the sum of photonic modes and excitonic resonances is used. Or a set of independent Hamiltonians, one for each photon mode, is chosen. Both are usually used equivalently for the same kind of multi-photonic systems which cannot be correct. However, identifying the suitable Hamiltonian is difficult when modeling experimental data. By means of numerical transfer matrix calculations, we demonstrate the scope of application of each approach: The first one holds only for the coupling of a single photon state to several excitons, while in the case of multiple photon modes, separate Hamiltonians must be used for each photon mode.