Hybridization of Surface Plasmon Polaritons and Molecular Excitations

Starke Kopplung von Molekülen mit einem räumlich begrenzten Lichtfeld führt zur Bildung neuer polaritonischer Eigenzustände des Systems, die sowohl molekulare als auch photonische Eigenschaften erhalten und somit ein großes Potenzial für Anwendungen in der Chemie und Optoelektronik besitzen. In dieser Arbeit wird die Kopplung zwischen Oberflächenplasmonen Polaritonen (SPPs), die als das räumlich begrenzte Lichtfeld agieren, und molekularen Anregungen wie Schwingungen und polaronischen Resonanzen untersucht. Das starke Kopplungsregime zwischen einer Molekülschwingung und einem SPP wird zum ersten Mal im mittleren Infrarot unter Verwendung der Carbonylschwingung von Poly(vinylmethylketon) Polymer und Silber als Ausbreitungsmedium von SPPs demonstriert. Die neu gebildeten Hybridmoden werden durch Experimente und numerische Modellierung untersucht, wobei Messungen der abgeschwächten Totalreflexion und der thermischen Emission sowie Berechnungen mittels der Transfermatrix und der linearen Dispersionstheorie verwendet werden. Ein Anticrossing in der Dispersion der Polariton-Zweige mit einer Energieaufspaltung bis zu 15 meV, was die Hauptsignatur des starken Kopplungsregimes ist, wird beobachtet. Die starke Kopplung mit Zinkgalliumoxid, einem hochdotierten Halbleiter als Alternative zu Edelmetallen, wird auch untersucht. Experimentelle und simulierte Reflektometrie-Spektren sowie Dispersionsrelationen werden diskutiert, um Rückschlüsse auf die Eigenschaften des Systems zu ziehen. Außerdem wird ein Ansatz zur Verbesserung der Leitfähigkeit organischer Halbleiterpolymere durch starke Kopplung ihrer polaronischen Zustände an SPPs vorgestellt und Leitfähigkeitsmessungen durchgeführt. Ziel ist es, die Delokalisierung der Hybridzustände auszunutzen, um die Leitfähigkeit zu verändern. Die präsentierten Ergebnisse bieten neue Einblicke in den Nutzen der Eigenschaften der Licht-Materie-Hybridisierung, um ihr volles Potenzial für verschiedene Bereiche und Anwendungen zu erforschen.Strong coupling of molecules with a confined light field results in the formation of new polaritonic eigenstates of the system called polaritons that inherit both molecular and photonic characteristics and thus holds strong potential for applications in chemistry and optoelectronics. In this work, coupling between propagating surface plasmon polaritons (SPPs), as confined light field, and molecular excitations, such as vibrational resonances and polaronic features, is investigated. The strong coupling regime between a molecular vibration and a propagating SPP is demonstrated for the first time in the mid-infrared spectral range using the carbonyl stretch vibration of Poly(vinyl methyl ketone) polymer and silver as metallic medium for SPPs propagation. The newly formed hybrid modes are investigated through experiments and numerical modelling, employing attenuated-total-reflection and thermal emission measurements as well as transfer-matrix and linear dispersion theory calculations. An anticrossing behavior in the dispersion of the polariton branches with an energy splitting up to 15meV, which is a key signature of the strong coupling regime, is observed. Strong coupling involving zinc gallium oxide, which is a highly doped semiconductor, as an alternative to noble metals is also investigated. Experimental and simulated reflectometry spectra as well as the dispersion relations are discussed so as to draw conclusions about the properties of the system. Furthermore, an approach to enhance the conductivity of organic semiconductor polymers by strongly coupling their polaronic states to SPPs is presented and four-point probe measurements are conducted. The goal is to exploit the delocalization of the hybrid states to alter the conductivity of the organic semiconductor. The results presented in this thesis provide new insights into the profit from the properties of light-matter hybridization in order to explore its full potential for several areas and applications

Trends of biosensing: plasmonics through miniaturization and quantum sensing

Despite being extremely old concepts, plasmonics and surface plasmon resonance-based biosensors have been increasingly popular in the recent two decades due to the growing interest in nanooptics and are now of relevant significance in regards to applications associated with human health. Plasmonics integration into point-of-care devices for health surveillance has enabled significant levels of sensitivity and limit of detection to be achieved and has encouraged the expansion of the fields of study and market niches devoted to the creation of quick and incredibly sensitive label-free detection. The trend reflects in wearable plasmonic sensor development as well as point-of-care applications for widespread applications, demonstrating the potential impact of the new generation of plasmonic biosensors on human well-being through the concepts of personalized medicine and global health. In this context, the aim here is to discuss the potential, limitations, and opportunities for improvement that have arisen as a result of the integration of plasmonics into microsystems and lab-on-chip over the past five years. Recent applications of plasmonic biosensors in microsystems and sensor performance are analyzed. The final analysis focuses on the integration of microfluidics and lab-on-a-chip with quantum plasmonics technology prospecting it as a promising solution for chemical and biological sensing. Here it is underlined how the research in the field of quantum plasmonic sensing for biological applications has flourished over the past decade with the aim to overcome the limits given by quantum fluctuations and noise. The significant advances in nanophotonics, plasmonics and microsystems used to create increasingly effective biosensors would continue to benefit this field if harnessed properly

Helicity Dependent Directional Surface Plasmon Polariton Excitation Using A Metasurface with Interfacial Phase Discontinuity

Surface plasmon polaritons (SPPs) have been widely exploited in various scientific communities, ranging from physics, chemistry to biology, due to the strong confinement of light to the metal surface. For many applications it is important that the free space photon can be coupled to SPPs in a controllable manner. In this Letter, we apply the concept of interfacial phase discontinuity for circularly polarizations on a metasurface to the design of a novel type of polarization dependent SPP unidirectional excitation at normal incidence. Selective unidirectional excitation of SPPs along opposite directions is experimentally demonstrated at optical frequencies by simply switching the helicity of the incident light. This approach, in conjunction with dynamic polarization modulation techniques, opens gateway towards integrated plasmonic circuits with electrically reconfigurable functionalities.Comment: 17 pages, 5 figures. Published on <Light:Science & Applications

Magneto-optical effects in hybrid plasmonic nanostructures

This thesis focuses on magneto-optical effects and their enhancement at optical resonances in hybrid plasmonic nanostructures. One of the main goals is to gain a better understanding of the transverse magnetic routing of light emission (TMRLE) regarding both components of the hybrid plasmonic-semiconductor model system used to investigate this novel effect. Here, the TMRLE describes the routing of light emitted from excitons in a diluted magnetic semiconductor (DMS) quantum well (QW), where the selection rules of the exciton optical transitions are modified by an external magnetic field to have a non-zero transverse spin along the magnetic field direction. By placing the light source near a surface, it can couple to subwavelength evanescent optical fields, such as surface plasmon polaritons (SPPs), which possess a strong transverse spin and spin-momentum locking. This translates the spin of the emitter into a routed wave along the surface and directional emission into the far-field. Firstly, the temperature dependence of the routing from the DMS QW, used as strongly polarizable light source, is investigated. The findings reveal a significant decline in the achievable emission routing for increasing temperatures, but also the emergence of the light-hole emission, which is routed in the opposite direction to the main heavy-hole emission. Additionally, alternative non-DMS-based QW structures are explored as potential candidates for achieving temperature-independent emission routing. Secondly, the influence of the plasmonic nanograting, the other constituent of the hybrid structure, on the enhanced routing is demonstrated. The emission directionality is investigated for various grating periods and slit widths, which also reveals the usually hard-to-detect weak coupling between the QW excitons and the SPPs as a large contributor to the emission directionality spectrum. Lastly, the thesis explores the transverse magneto-optical Kerr effect (TMOKE) for light reflected from or transmitted through a magnetite-based plasmonic waveguide structure. Here, the hybridization of the plasmonic and magnetic waveguide modes leads to a wide-band enhancement of the TMOKE signal in transmission.Der Fokus dieser Arbeit liegt auf magneto-optischen Effekten und deren Verstärkung an optischen Resonanzen in hybriden plasmonischen Nanostrukturen. Eines der Hauptziele ist das bessere Verständnis der transversalen magnetischen Lenkung der Lichtemission (TMRLE) bezüglich beider Komponenten des hybriden plasmonischen Halbleiter-Modellsystems, an dem dieser neuartige Effekt untersucht wird. Hier beschreibt der TMRLE die direktionale Lenkung der Lichtemission von Exzitonen aus einem semimagnetischen Halbleiter (DMS) Quantentopf (QW), wobei die Auswahlregeln der optischen Exzitonen-Übergänge von einem externen Magnetfeld so modifiziert werden, dass sie einen transversalen Spin entlang des Magnetfeldes haben. Wird diese Lichtquelle nahe einer Oberfläche platziert, so kann sie an evaneszente optische Felder mit starkem transversalem Spin und einer Kopplung von Spin und Ausbreitungsrichtung, wie Oberflächenplasmonpolaritonen (SPPs), koppeln. Dadurch wird der Emitterspin in eine direktionale Welle entlang der Oberfläche übersetzt, die dann direktional in das Fernfeld emittieren kann. Zunächst wird die Temperaturabhängigkeit der Emissionslenkung aus dem DMS QW untersucht, welcher als stark polarisierbare Lichtquelle fungiert. Dabei zeigt sich eine starke Abnahme der erreichbaren Emissionslenkung bei steigenden Temperaturen, aber auch der aufkommende Beitrag der Leichtloch-Emission, welche in die entgegengesetzte Richtung der primären Schwerloch-Emission gelenkt wird. Außerdem werden alternative nicht-DMS-basierte QW Strukturen als Kandidaten für eine temperaturunabhängige Emissionslenkung untersucht. Zweitens wird der Einfluss des plasmonischen Nanogitters als weiterer Bestandteil der Hybridstruktur auf die verstärkte Emissionslenkung gezeigt. Dafür wird die Emissionsdirektionalität für verschiedene Gitterperioden und -spaltbreiten untersucht, wobei auch die sonst schwer zu detektierende schwache Kopplung der QW-Exzitonen und SPPs als großer Beitrag zum Direktionalitätsspektrum aufgedeckt wird. Zuletzt wird noch der transversale magneto-optische Kerr-Effekt (TMOKE) für reflektiertes und transmittiertes Licht von einer Magnetit-basierten plasmonischen Nanostruktur untersucht. Hier führt die Hybridisierung der plasmonischen und der magnetischen Wellenleitermoden zu einer breitbandigen Verstärkung des TMOKE Signals in Transmission

Single-molecule Detection in Nanogap-embedded Plasmonic Gratings

We introduce nanogap-embedded silver plasmonic gratings for single-molecule (SM) visualization using an epifluorescence microscope. This silver plasmonic platform was fabricated by a cost-effective nano-imprint lithography technique, using an HD DVD template. DNA/RNA duplex molecules tagged with Cy3/Cy5 fluorophores were immobilized on SiO2-capped silver gratings. Light was coupled to the gratings at particular wavelengths and incident angles to form surface plasmons. The SM fluorescence intensity of the fluorophores at the nanogaps showed approximately a 100-fold mean enhancement with respect to the fluorophores observed on quartz slides using an epifluorescence microscope. This high level of enhancement was due to the concentration of surface plasmons at the nanogaps. When nanogaps imaged with epifluorescence mode were compared to quartz imaged using total internal reflection fluorescence (TIRF) microscopy, more than a 30-fold mean enhancement was obtained. Due to the SM fluorescence enhancement of plasmonic gratings and the correspondingly high emission intensity, the required laser power can be reduced, resulting in a prolonged detection time prior to photobleaching. This simple platform was able to perform SM studies with a low-cost epifluorescence apparatus, instead of the more expensive TIRF or confocal microscopes, which would enable SM analysis to take place in most scientific laboratories

Optical Properties of Hybrid Nanomaterials

abstract: The interaction of light with nanoscale structures consisting of metal and two-level quantum emitters is investigated computationally. A method of tilting the incoming electromagnetic wave is used to demonstrate coupling between a sinusoidal grating and two-level quantum emitters. A system consisting of metallic v-grooves and two-level emitters is thoroughly explored in the linear regime, where the spatially uniform fields provide a unique means of characterizing the coupling between the v-grooves and emitters. Furthermore, subwavelength spatial effects in the ground state population of emitters in the v-grooves are observed and analyzed in the non-linear regime. Finally, photon echoes are explored in the case of a one-dimensional ensemble of interacting two-level emitters as well as two-level emitters coupled to metallic slits, demonstrating the influence of collective effects on the echo amplitude in the former and the modifcation of the photon echo due to interaction with surface plasmons on the slits in the latter.Dissertation/ThesisDoctoral Dissertation Physics 201

Interactions between excitation and extraction modes in an organic-based plasmon-emitting diode

International audienceThis study demonstrates the feasibility of enhancing an organic-based plasmon-emitting diode on the directional light beaming efficiency by near-field surface plasmon polaritons (SPPs) in both metal grating and polymer grating nanostructures. The interaction between organic/metal and PR/metal interfaces to cause SPPs can facilitate specific directional emission. Directional emission properties give rise to a spectral band-gap response enhancement. Our results also verify that efficient surface plasmon grating coupled emissions (SPGCEs) can improve directionality under index-mediated tuning. Experimental results indicate SP decoupling emission in the visible light. The subsequent emission intensity can increase by up to 3.5 times. Moreover, a narrow FWHM of approximately 60 nm in a defined direction is achieved, and an SP coupling rate is approximately 80% on the metal grating structure. The proposed method is highly promising for use as an active plasmonic emitter and discoloration biosensors with enhanced SPPs resonance energy, owing to interactions with the organic/metal nanostructur

Plasmonic Antennas Hybridized with Dielectric Waveguides

For the purpose of using plasmonics in an integrated scheme where single emitters can be probed efficiently, we experimentally and theoretically study the scattering properties of single nano-rod gold antennas as well as antenna arrays placed on one-dimensional dielectric silicon nitride waveguides. Using real space and Fourier microscopy correlated with waveguide transmission measurements, we quantify the spectral properties, absolute strength and directivity of scattering. The scattering processes can be well understood in the framework of the physics of dipolar objects placed on a planar layered environment with a waveguiding layer. We use the single plasmonic structures on top of the waveguide as dipolar building blocks for new types of antennas where the waveguide enhances the coupling between antenna elements. We report on waveguide hybridized Yagi-Uda antennas which show directionality in out-coupling of guided modes as well as directionality for in-coupling into the waveguide of localized excitations positioned at the feed element. These measurements together with simulations demonstrate that this system is ideal as a platform for plasmon quantum optics schemes as well as for fluorescence lab-on-chip applications

Efficient out-coupling and beaming of Tamm optical states via surface plasmon polariton excitation

We present evidence of optical Tamm states to surface plasmon polariton (SPP) coupling. We experimentally demonstrate that for a Bragg stack with a thin metal layer on the surface, hybrid Tamm-SPP modes may be excited when a grating on the air-metal interface is introduced. Out-coupling via the grating to free space propagation is shown to enhance the transmission as well as the directionality and polarization selection for the transmitted beam. We suggest that this system will be useful on those devices, where a metallic electrical contact as well as beaming and polarization control is needed