Esta tesis describe el diseño, la fabricación y la caracterización óptica de sistemas plasmónicos resonantes capaces de confinar y aumentar campos de luz en la escala manométrica. En primer lugar, se utilizaron modelos numéricos 3D para diseñar diferentes geometras de nanoestructuras plasmónicas acopladas, a través del cálculo de la respuesta óptica de su campo lejano y cercano. Sobre la base de estas simulaciones se fabricaron las nanoestructuras por litografía de haz electrónico. Se puso especial énfasis en el aumento de la resolución y la optimización de la reproducibilidad de parámetros críticos como la forma de las partículas y el gap entre ellas. Por último, se empleó espectroscopía de campo lejano combinada con espectroscopía de luminiscencia inducida por dos fotones (TPL) para sondar la respuesta óptica local de las geometrías optimizadas. Hemos centrado nuestra atención en diferentes tipos de estructuras metálicas: dímeros, antenas con gap, conjuntos finitos de partículas en cadenas y en forma de estrella. Los dímeros tienen una fuerte amplificación del campo en su gap nanométrico por el acoplamiento en campo cercano de sus resonancias plasmonicas dipolares. Análogamente, antenas con gap, formadas por dos barras de oro adyacentes que soportan resonancias multipolares, pueden acoplar de manera eficiente la luz y concentrarla en volúmenes pequeños. Se ha demostrado que cadenas finitas de partículas son buenos candidatos para guiar la luz a través de secciones transversales por debajo de la longitud de onda y aquí demostramos que también se pueden utilizar como nanolentes capaces de concentrar la luz en su extremo. La distribución del campo cercano en conjuntos de partículas de oro en forma de estrella presenta una fuerte dependencia con la polarización del campo incidente que puede ser explotada para dirigirse dinámicamente a nano-objetos. La espectroscopía de campo lejano de conjuntos de dímeros y de cadenas finitas de partculas se comparó con la espectroscopía de TPL. Nuestro principal resultado es mostrar que la TPL es preferentemente sensible a los campos locales, permitiendo evaluar características espectrosc ópicas que no podrían resolverse de otro modo. A fin de superar las limitaciones de las medidas de conjuntos, en una segunda etapa se dedicó un considerable esfuerzo a construir y optimizar un montaje óptico para medir la señal de TPL de estructuras únicas. El uso de la micro-espectroscopía de TPL permitió obtener mapas espectrales de los modos de antenas aisladas con resolución espacial. Como se predijo mediante cálculos, hemos sido capaces de visualizar directamente, en la resonancia, la señal de TPL amplificada dentro del gap. Nuestros resultados muestran cómo las medidas de TPL pueden compararse directamente con la distribución de la cuarta potencia del campo local calculado. Mediante el análisis de la evolución de la señal de TPL en función de la longitud de onda incidente en el gap y en las extremidades de la antena tenemos más conocimiento sobre el mecanismo físico detrás de la resonancia de la antena. Finalmente, la microscopía de TPL se utilizó para sondar el campo cercano para diferentes orientaciones de la polarización lineal incidente sobre los conjuntos de partículas en forma de estrella. Se demuestra que, a diferencia del espectro de dispersión, la distribución de TPL en la estructura depende drásticamente del estado de polarización incidente. Nuestro estudio aporta una contribución significativa al campo de la óptica de plasmones, proponiendo nuevas geometrías para confinar de manera eficiente los campos ópticos a la escala nanometrica, aportando un profundo conocimiento sobre el uso de micro-espectroscopa de TPL como sonda óptica local. Nuestros resultados tendrán importancia en aplicaciones tales como espectroscopía mejorada, biosensores y la interacción luz-materia, donde se necesita evaluar el campo experimentado por una pequeña cantidad de materia cercana a la nanoestructura. / This thesis describes the design, fabrication and the optical characterization of plasmon-resonant systems able to confine and enhance light fields down to the sub-wavelength scale. Extensive 3D numerical modeling was first used to design different geometries of coupled plasmonic nanostructures through the calculation of their far-field and near-field optical response. On the basis of simulations, the nanostructures were fabricated by e-beam lithography and thin film deposition. Special efforts were devoted to increasing the resolution and optimizing the reproducibility of critical parameters such as particle shape and interparticle gaps. Finally, far-field spectroscopy combined with two-photon induced luminescence (TPL) spectroscopy was used to probe the local optical response of the optimized architectures. We focused our attention on different families of structures: metal dimers, bar antennas, finite chains of nanoparticles and star-like particle arrangements. Particle dimers feature strong field enhancements in their sub-wavelength gap due to near-field coupling of their dipolar localized plasmon resonances. Based on the same physics, gap antennas, formed by two adjacent gold bars supporting multipolar resonances can efficiently couple to propagating light and concentrate it into tiny volumes. While finite particle chains were previously shown by other authors to be good candidates to guide light through subwavelength cross-sections, we show here that they can also be used as efficient nanolenses able to concentrate light at their extremity. Finally, the near-field distribution in star-like arrangements of gold nanoparticles exhibits a strong dependence with the incident field polarization which can be exploited for dynamical optical addressing of nano-objects. We have compared the far field spectroscopy of large ensembles of dimers and finite chains to TPL spectroscopy. Our main result is to show that TPL is preferentially sensitive to local fields and that it enables the assessment of spectroscopic features which cannot be resolved otherwise. In order to overcome the limitations of measurements on large ensembles a considerable effort was dedicated to mounting and optimizing an optical set-up enabling TPL measurement of single structures. Using the developed TPL micro-spectroscopy, spatially resolved spectral mode mapping on single resonant gap-antennas was achieved. As predicted by calculations, we were able to directly visualize at resonance the strongly enhanced TPL signal within the gap. Our results show how TPL scans can be directly compared with the convoluted distribution of the fourth power of the calculated local mode field. By monitoring the evolution with the incident wavelength of the TPL signal within the gap and at the antenna extremities we got further insight in the physical mechanism behind the buildup of the antenna’s resonance. Finally, TPL microscopy was used to probe the local fields under different orientations of the incident linear polarization near star-like arrangement of gold disks. It is shown that, unlike the scattering spectrum, the TPL distribution over the structure is found to depend drastically on the incident polarization state. Our study brings a significant contribution to the field of Plasmon optics by proposing novel geometries able to efficiently confine optical fields down to the nanometric scale, but also by providing deep insight into the use of TPL microspectroscopy to probe their local optical response. Our findings are foreseen to be important in applications such as enhanced spectroscopy, bio-sensing and enhanced light-matter interaction, where one needs to assess the actual field experienced by small amounts of matter.

Atherosclerosis and specifically rupture of vulnerable plaques account for 23% of all deaths worldwide, far surpassing both infectious diseases and cancer. Plaque-based macrophages, often associated with lipid deposits, contribute to atherogenesis from initiation through progression, plaque rupture and ultimately, thrombosis. Therefore, the macrophage is an important early cellular marker related to vulnerability of atherosclerotic plaques. The objective of my research is to assess the ability of multiple optical imaging modalities to detect, and further characterize the distribution of macrophages (having taken up plasmonic gold nanoparticles as a contrast agent) and lipid deposits in atherosclerotic plaques. Tissue phantoms and macrophage cell cultures were used to investigate the capability of nanorose as an imaging contrast agent to target macrophages. Ex vivo aorta segments from a rabbit model of atherosclerosis after intravenous nanorose injection were imaged by optical coherence tomography (OCT), photothermal imaging (PTW) and two-photon luminescence microscopy (TPLM), respectively. OCT images depicted detailed surface structure of atherosclerotic plaques. PTW images identified nanorose-loaded macrophages (confirmed by co-registration of a TPLM image and corresponding RAM-11 stain on a histological section) associated with lipid deposits at multiple depths. TPLM images showed three-dimensional distribution of nanorose-loaded macrophages with a high spatial resolution. Imaging results suggest that superficial nanorose-loaded macrophages are distributed at shoulders on the upstream side of atherosclerotic plaques at the edges of lipid deposits. Combination of OCT with PTW or TPLM can simultaneously reveal plaque structure and composition, permitting assessment of plaque vulnerability during cardiovascular interventions. / text

Raman spectroscopy is a promising technique because it contains abundant vibrational chemical information. However, Raman spectroscopy is restricted by its small scattering cross section, and many techniques have been developed to amplify Raman scattering intensity. In this dissertation, I study two of these techniques, coherent Raman scattering and surface enhanced Raman scattering and discuss their properties. In the first part of my dissertation, I investigate two coherent Raman processes, coherent anti-Stokes Raman scattering (CARS) and stimulated Raman scattering (SRS). In CARS project, I mainly focus on the molecular resonance effect on detection sensitivity, and I find the detection sensitivity can be pushed into 10 [micromolar] with the assistance of molecular resonance. Also, I am able to retrieve background-free Raman spectra from nonresonant signals. For SRS, we develop a new SRS system by applying spectral focusing mechanism technique. We examine the feasibility and sensitivity of our SRS system. The SRS spectra of standards obtained from our system is consistent with literature, and the sensitivity of our system can achieve 10 times above shot-noise limit. In second part of this dissertation, I study surface enhanced Raman scattering (SERS) and related plasmonic effects. I synthesize different shapes of nanoparticles, including nanorod, nanodimer structure with gap and pyramids by template method, and study how electric field enhancement effects correlate to SERS by two photon luminescence (TPL). Also, I build an optical system to study optical image, spectra and particle morphology together. I find that SERS intensity distribution is inhomogeneous and closely related to nanoparticle shape and polarization direction. However, TPL and SERS are not completely correlated, and I believe different relaxation pathways of TPL and SERS and coupling of LSPR and local fields at different frequencies cause unclear correlation between them. / text