Afin de développer des capteurs ultrasensibles des substrats fiables pour la diffusion Raman exaltée de surface (SERS) ont été fabriqués. Les deux meilleurs candidats de matériaux constituant les nanoparticules pour des substrats SERS sont l’argent et l’or. L’argent présente un meilleur facteur d’exaltation de l'intensité Raman et l’or est stable dans les milieux biologiques. C’est pourquoi la combinaison de ces deux métaux dans des nanostructures bimétalliques semble être une approche prometteuse qui combine les propriétés de surface de l’or et d’exaltation de l’argent. Le recuit thermique des couches métalliques minces est utilisé comme une technique simple et peu coûteuse. Cette dernière permet d’élaborer des substrats homogènes et reproductibles de nanoparticules bimétalliques or-argent ayant un facteur d’exaltation importante. Ces nanoparticules gardent leurs propriétés d’exaltation même après une année de fabrication. En jouant sur la composition de nanoparticules bimétalliques il est possible d’avoir une résonance de plasmons de surface localisés (LSPR) sur tout le spectre visible. Ces substrats sont caractérisés par une exaltation SERS supérieure lorsque la résonance plasmon est plus proche de la longueur d'onde d'excitation Raman. En outre, les nanoparticules bimétalliques de différentes tailles, compositions ont été réalisés par lithographie électronique. L’étude systématique de leurs propriétés plasmoniques et de leur exaltation SERS a révélé une conservation du lien entre résonance plasmon et signal SERS / Driven by the interest in finding ultrasensitive sensors devices, reliable surface enhanced Raman scattering (SERS) based substrates are fabricated. Silver and gold nanoparticles are two of the best candidates for SERS substrates where Ag nanoparticles exhibit large enhancing ability in Raman intensity while Au nanostructures are stable in biological systems. Hence, combining the two metals in bimetallic nanostructures appeared to be a promising approach in order to sum the merits of Au surface properties and Ag enhancing ability. Thermal annealing of thin metallic films is used as a simple and relatively inexpensive technique to elaborate homogenous and reproducible Ag/Au bimetallic nanoparticles SERS substrates with high enhancing ability. The fabricated nanoparticles proved their enhancing stability even after one year of fabrication. Manipulating the composition of Ag/Au bimetallic NPs resulted in tuning the Localized Surface Plasmon Resonance (LSPR) over the whole visible spectrum, where the substrates are characterized with higher SERS enhancement when they exhibit LSPR closer to the Raman excitation wavelength. Additionally, bimetallic nanoparticles patterns with different size, composition and lattice constants have been conducted by electron beam lithography. The systematic study of their interesting plasmonic and SERS enhancing properties revealed maintenance in the LSPR-SERS relation by changing the nanoparticle size

Les avancées récentes de la nanofabrication ont permis de faire émerger un nouveau champ de recherche, celui des nanocapteurs. En particulier, le nanocapteur plasmonique dont le principe utilise l’effet SERS (Diffusion Raman Exaltée de Surface) commence à s’imposer. En effet, ce capteur permet d’amplifier la signature d’une molécule jusqu’à un facteur de 1012 et fournit une véritable empreinte digitale de chaque molécule. La sensibilité du capteur dépend des propriétés optiques des Nanoparticules Métalliques (NPMs) qui sont liées aux propriétés physiques et structurales de ces dernières. Ainsi, la maîtrise de la fabrication de NPMs est un réel défit pour des multiples applications nanotechnologiques. Dans ce contexte, nous avons développé une approche originale de fabrication de NPMs organisées par auto-assemblage de polymère. Il s’agit d’introduire de manière contrôlée des interactions physiques qui se manifestent lors de la fabrication par une nano-séparation de phase au sein du matériau. Ceci se traduit par un nanstructuration du polymère et une auto-organisation très spécifique du précurseur métallique qui se transforme spontanément en NPMs. Les investigations expérimentales en considérant les différents facteurs physico-chimiques impliqués, nous ont permis d’identifier les paramètres clés de cette structuration et de hiérarchiser leur influence sur les dimensions structurales et la réponse optique des NPMs. Finalement, la capacité du nanocapteur à détecter de faibles traces (<10-13 M) de polluants organiques a été démontrée / The recent advances in nanofabrication techniques have allowed for the emergence of novel sensing approaches. Amongst these various approaches, Surface Enhanced Raman Spectroscopy (SERS) via the use of plasmonic substrates has received wide-spread attention due to its many interesting proper-ties. In fact, plasmonic substrates enhance the Ra-man signal up to 12 orders of magnitude, paving the path for single molecule detection. Nevertheless, the sensitivity of this technique is strongly affected by the physical and structural properties of the metallic nanoparticles (MNPs). Thus, the mastering of the MNPs fabrication is a major challenge for various nanotechnological applications.In this context, we have developed a novel approach for the fabrication of organized NMPs through poly-mer self-assembly. The fabrication technique con-sists on controlling the physical interactions which occur during the fabrication through a nanophase separation in the polymer solution. This results in a nanostructuring of the polymer and a strong self-organization of the metallic precursor which is rapidly reduced into the MNPs. Experimental investigations of the different physical and chemical processes in play allow for a better understanding of the various keystone parameters of the nanostructuring as well as for determining their influences on the dimensions and optical response of MNPs. Finally, the fabricated plasmonic substrate demonstrated SERS limits of detection down to 10-13 M

La plasmonique hybride est un sujet d’actualité qui exploite des interactions physiques entre nano-objets métalliques et d’autres nanomatériaux. En bénéficiant des propriétés de chacun de leurs constituants, les nanostructures hybrides sont utilisées dans de nombreuses applications comme la détection d’espèces bio-chimiques. Dans cette thèse, nous présentons une nouvelle nanostructure hybride polymère/metal qui est non seulement utilisée comme nano-émetteur anisotrope qui s’avère aussi être un outil puissant de caractérisation du champ proche optique.La fabrication de cette nouvelle nanostructure est basée sur une approche de par photopolymérisation à l’échelle nanométrique. Cette technique, en comparaison aux méthodes traditionnelles de caractérisation, ne fournit pas seulement l’image de la distribution du champ, mais permet aussi des mesures quantitatives des plasmons de surface avec une résolution sub -5nm, incluant une description fine de la décroissance exponentielle des ondes évanescentes impliquées.A l’aide du mode plasmon dipolaire, une distribution anisotrope de matériau organique est intégrée dans le voisinage de la nanoparticule métallique. Avec une haute concentration de molécules de colorant dans le polymère, l’intensité des signaux de fluorescence et Raman du nano-émetteur hybride dépend de la polarisation incidente. À notre connaissance, il s’agit de la première réalisation d’un nano-émetteur dont le milieu à gain présente une distribution spatiale complexe le rendant sensible à la polarisation / Hybrid plasmonics has given rise to increasing interest in the context of the interaction between metal nano-objects and other materials. By benefiting from each of its constituents, hybrid nanostructures are commonly adopted in studies and optimization of biological and chemical sensors, nanoparticle with high plasmon resonance tunability, and nano-emitters. This PhD thesis presents a hybrid nanostructure of photopolymer/metal nanoparticle that is used as a near-field characterizing tool and as an anisotropic nano-emitter.The fabrication of this hybrid nanostructure is a near-field imprinting process based on nanoscale photopolymerization. This technique, compared with traditional near-field characterization methods, provides not only the image of the field distribution, but also enables quantification of the surface plasmon properties with sub-5nm resolution and reproduction of the exponential decay of the near-field.Under dipolar mode plasmon, the photopolymer was created anisotropically in the vicinity of the metal nanoparticle. With high concentration of dye molecules trapped in the polymer, the hybrid nano-emitter displays surface enhanced fluorescence and Raman signal that is dependent on the incident polarization. To our knowledge, this is the first achievement of the anisotropic nano-emitter based on the inhomogeneous distribution of the active molecule

This dissertation investigates two long standing issues in nonlinear optics: complete characterization of the ultrafast dynamics of simple molecules, and the potential of a two-photon laser using a bulk semiconductor gain medium. Within the Born-Oppenheimer approximation, nonlinear refraction in molecular liquids and gases can arise from both bound-electronic and nuclear origins. Knowledge of the magnitudes, temporal dynamics, polarization and spectral dependences of each of these mechanisms is important for many applications including filamentation, white-light continuum generation, all-optical switching, and nonlinear spectroscopy. In this work the nonlinear dynamics of molecules are investigated in both liquid and gas phase with the recently developed beam deflection technique which measures nonlinear refraction directly in the time domain. Thanks to the utility of the beam deflection technique we are able to completely determine the third-order response function of one of the most important molecular liquids in nonlinear optics, carbon disulfide. This allows the prediction of essentially any nonlinear refraction or two-photon absorption experiment on CS2. Measurements conducted on air (N2 and O2) and gaseous CS2 reveal coherent rotational revivals in the degree of alignment of the ensemble at a period that depends on its moment of inertia. This allows measurement of the rotational and centrifugal distortion constants of the isolated molecules. Additionally, the rotational contribution to the beam deflection measurement can be eliminated thanks to the particular polarization dependence of the mechanism. At a specific polarization, the dominant remaining contribution is due to the bound-electrons. Thus both the bound-electronic nonlinear refractive index of air, and second hyperpolarizability of isolated CS2 molecules, are measured directly. The later agrees well with liquid CS2 measurements, where local field effects are significant. The second major portion of this dissertation addresses the possibility of using bulk semiconductors as a two-photon gain medium. A two-photon laser has been a goal of nonlinear optics since shortly after the original laser*s development. In this case, two-photons are emitted from a single electronic transition rather than only one. This processes is known as two-photon gain (2PG). Semiconductors have large two-photon absorption coefficients, which are enhanced by ~2 orders of magnitude when using photons of very different energies, e.g., ћωa≈10ћωb. This enhancement should translate into large 2PG coefficients as well, given the inverse relationship between absorption and gain. Here, we experimentally demonstrate both degenerate and nondegenerate 2PG in optically excited bulk GaAs via pump-probe experiments. This constitutes, to my knowledge, the first report of nondegenerate two-photon gain. Competition between 2PG and competing processes, namely intervalence band and nondegenerate three-photon absorption (ND-3PA), in both cases are theoretically analyzed. Experimental measurements of ND-3PA agree with this analysis and show that it is enhanced much more than ND-2PG. It is found for both degenerate and nondegenerate photon pairs that the losses dominate the two-photon gain, preventing the possibility of a two-photon semiconductor laser.

Made available in DSpace on 2016-03-15T19:37:41Z (GMT). No. of bitstreams: 1 Jair Fiuza - EE2006.pdf: 870543 bytes, checksum: 939198dd0585c5cbae3d86adf6c858cc (MD5) Previous issue date: 2006-08-29 / The performance of a distributed Raman amplifier at S - Band using the TrueWave® Reach Low Water Peak fiber in a 100km span is analyzed through numerical simulations. The manufacturer, the OFS Fitel Denmark Ap, has experimentally characterized the physical parameters of the fiber, such as, attenuation, dispersion and Raman gain efficiency at Band - S. The low fiber attenuation around pump wavelength region, around 0,34dB/km at 1370nm, allow the achievement of approximately 10dB over 70nm in the S - Band &#8722; using 4 (four) pump lasers with pump power on the order of tenth of mWatts . / O desempenho de um amplificador Raman distribuído na Banda - S utilizando a fibra óptica TrueWave® Reach Low Water Peak em um enlace de 100km é analisado através de simulações numéricas. O fabricante, a OFS Fitel Denmark Ap, caracterizou experimentalmente os parâmetros físicos da fibra óptica, tais como atenuação, dispersão, e eficiência de ganho Raman na Banda - S. A baixa absorção dessa fibra óptica na região espectral onde se localizam os lasers de bombeamento, em torno de 0,34dB/km, para 1370nm, permite a utilização de 4 lasers de bombeamento com potências da ordem de dezenas de mWatts, para garantir um ganho on-off da ordem de 10dB em 70nm (1460 a 1530nm) na Banda - S.

Raman spectroscopy involves change in the polarizability of the molecular system on excitation and is based on scattering process. Spontaneous Raman scattering is a two photon process, in which the input light initiates the excitation, which then leads to an emission of another photon due to scattering. It is extensively used to understand molecular properties. As spontaneous Raman scattering is a weak process, the detection of these weak Raman photons are rather difficult. Alternatively, resonance Raman (RR) scattering is another technique where the excitation wavelength is chosen according to the material under study. The excitation wavelength is chosen to be within the absorption spectrum of the material under study. RR spectroscopy not only provides considerable improvement in the intensity of the Raman signal, but also provides mode specific information i.e. the modes which are Franck-Condon active in that transition can be observed. There are reports on RR studies of many systems using pulsed light as an excitation source. It is necessary to use at least two pulsed laser sources for carrying out the time resolved RR spectroscopy. A single pulse source for excitation would lead to compromise either with temporal or spectral resolution which is due to the uncertainty principle. If an excitation pulse has pulse width of ~100 femtoseconds then the spectral resolution will be ~ 150 cm-1. It is clear now that for improving the temporal and spectral resolution simultaneously, usage of single pulse for Raman experiments (spontaneous scattering) is not adequate. The usage of multiple laser pulses may provide the way out to improve the resolutions. Nonlinear spectroscopy in a broad view helps in understanding the structural and dynamical properties of the molecular systems in a deeper manner. There are a number of techniques as a part of nonlinear spectroscopy that have emerged in due course to meet different requirements and to overcome some difficulties while understanding the molecular properties. Stimulated Raman (SRS) gain, coherent anti-Stokes Raman scattering (CARS) and the inverse Raman spectroscopy are a few to mention as third order nonlinear spectroscopic techniques which give the similar kind of information about the molecular systems. Stimulated Raman scattering is a more general process involved in nonlinear Raman processes. SRS involves at least two laser pulses and the difference in their frequencies should match with the vibrational frequency of the molecule. The polarization has to be matched between the Raman pump and the Raman probe pulses. We have developed a new nonlinear Raman technique in our laboratory named as ultrafast Raman loss spectroscopy (URLS) using the principles of nonlinear Raman scattering. It involves the Raman pump (~ 1 picosecond (ps) or ~ 15 cm-1spectral resolution) and Raman probe as a white light continuum (100 fs) whose frequency components ranges from 400-900 nm. The laser system consists of Tsunami which is pumped by a Millennia laser and Spitfire-Pro, a regenerative amplifier which is pumped by an Empower laser. Tsunami provides a 100 fs, 780 nm centered, 80 MHz and ~6 nJ energy laser pulses. The Tsunami output is fed into Spitfire to amplify its energy and change the repetition rate to 1 KHz. The pulse length of the input pulse is preserved in amplification. The output of amplifier is split into two equal parts; one part is used to pump the Optical Parametric Amplifier (OPA) in order to generate wavelengths in the range 480-800 nm. The output of the OPA is utilized to generate Raman pump which has to be in ps in order to get the best spectral resolution. A small portion of the other part of amplifier output is utilized to generate white light source for the Raman probe. The remaining part of the amplifier output is used to pump TOPAS to generate wavelengths in the ultraviolet region. URLS has been applied to many molecular systems which range from non-fluorescent to highly fluorescent. URLS has been demonstrated to be very sensitive and useful while dealing with highly fluorescent systems. URLS is a unique technique due to its high sensitivity and the Raman loss signal intensity is at least 1.5-2 times higher as compared to the Raman gain signal intensities. Cresyl violet perchlorate (CVP) is a highly fluorescent system. URLS has been applied to study CVP even at resonance excitation. Rhodamine B has also been studied using URLS. Spontaneous Raman scattering is very difficult to observe experimentally in such high quantum yield fluorescent systems. The variation in the lineshapes of the Raman bands for different RP excitation wavelengths in URLS spectra shows the mode dependent behavior of the absorption spectrum. The experimental observation of variation in the lineshape has been accounted using theoretical formalism. The thesis is focused on discussing the development of the new nonlinear Raman spectroscopic technique URLS in detail and its applicability to molecular systems for better understanding. A theoretical formalism for accounting the uniqueness of URLS among the other nonlinear Raman techniques is developed and discussed in various pictorial representations i.e. ladder, Feynman and closed loop diagrams. A brief overview of nonlinear spectroscopy and nonlinear Raman spectroscopy is presented for demonstrating the difference between the URLS and the other nonlinear Raman techniques.