Desde a sua origem nos laboratórios do Bell Labs, durante a década de 70, pinças ópticas vêm sendo investigadas, desenvolvidas e diversificadas por vários grupos nacionais e internacionais incluindo, nos últimos anos, o nosso departamento (Departamento de Engenharia Elétrica e de Computação - SEL/EESC/USP) e, em particular, o Grupo de Telecomunicações a ele vinculado, com propostas de aplicações em óptica biomédica e medicina. Dada a importância deste assunto, o principal objetivo deste trabalho é estender a análise teórica de forças ópticas utilizando uma descrição simples, porém eficaz, e analítica de um feixe de Bessel truncado, isto é, gerado por abertura finita. Até onde sabemos, esta é a primeira tentativa de introduzir esta investigação dos feixes originais de Durnin na literatura, e, deste modo, temos a possibilidade de contribuir com uma análise inédita de um feixe de Bessel com características físicas reais. Com a modelagem matemática dos feixe de Bessel truncados em mãos, aplicamos o cálculo de forças nos regimes de óptica geométrica e de Rayleigh e analisamos o seu comportamento quando os feixes incidem em espalhadores dielétricos esféricos. Como resultado direto deste trabalho, publicamos dois artigos descrevendo as forças ópticas no regime de óptica geométrica e de Rayleigh que um feixe de Bessel truncado causa em uma partícula dielétrica esférica. Como resultados indiretos, publicamos dois artigos com os mesmos cálculos de forças, adotando classe de feixes chamada Frozen-Waves, que é uma superposição de feixes de Bessel de mesma frequência. / Since its origins at Bell Labs laboratories, during the 1970s, optical tweezers have been researched, developed and diversified by several research groups, both nationally and internationally, including in our department (Department of Electrical and Computing Engineering - SEL/EESC/USP), in particular the Telecom Group associated to it, with several proposals with applications of optical tweezers in different fields from medicine to biomedical optics. Given the importance of this field, our main goal is to extend the theoretical analysis of optical forces using a simplest - but effective - analytical description of truncated Bessel beams (i.e. beams that are generated by finite apertures). As far we know, this is the first attempt to introduce such analysis of the originals Durnin beams in the literature, thus, we may have the chance to contribute to an unpublished study of a truncated Bessel beam with real characteristics. With such mathematical model at hands, we calculate the forces exerted by the truncated Bessel beam in ray optics and Rayleigh regime and analyze their behavior when hits dielectric spherical particles. As direct result of this work, we have published two papers describing the optical forces in ray optics and Rayleigh regime that a truncated Bessel beam causes in a spherical dielectric particle. As indirect results, we have published two papers with the same force considerations, adopting a beam class called Frozen-Waves, which is a superposition of same frequency Bessel beams.

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The two main themes in this thesis are the implementation of interference methods with optically trapped particles for measurements of position and optical phase (optical interferometric metrology) and the optical manipulation of nanoparticles for studies in the assembly of nanostructures, nanoscale heating and nonlinear optics (nanophotonics). The first part of the thesis (chapter 1, 2) provides an introductory overview to optical trapping and describes the basic experimental instrument used in the thesis respectively. The second part of the thesis (chapters 3 to 5) investigates the use of optical interferometric patterns of the diffracting light fields from optically trapped microparticles for three types of measurements: calibrating particle positions in an optical trap, determining the stiffness of an optical trap and measuring the change in phase or coherence of a given light field. The third part of the thesis (chapters 6 to 8) studies the interactions between optical traps and nanoparticles in three separate experiments: the optical manipulation of dielectric enhanced semiconductor nanoparticles, heating of optically trapped gold nanoparticles and collective optical response from an ensemble of optically trapped dielectric nanoparticles.

Optical trapping of metal nanoparticles investigates phenomena at the interface of plasmonics and optical micromanipulation. This thesis combines ideas of optical properties of metals originating from solid state physics with force mechanism resulting from optical trapping. We explore the influence of the particle plasmon resonance of gold and silver nanospheres on their trapping properties. We aspire to predict the force mechanisms of resonant metal particles with sizes in the Mie regime, beyond the Rayleigh limit. Optical trapping of metal nanoparticles is still considered difficult, yet it provides an excellent tool to investigate their plasmonic properties away from any interface and offers opportunities to investigate interaction processes between light and nanoparticles. Due to their intrinsic plasmon resonance, metal nanoparticles show intriguing optical responses upon interaction with laser light. These differ greatly from the well-known bulk properties of the same material. A given metal nanoparticle may either be attracted or repelled by laser light, only depending on the wavelength of the latter. The optical forces acting on the particle depend directly on its polarisability and scattering cross section. These parameters vary drastically around the plasmon resonance and thus not only change the magnitude but also the direction and entire nature of the acting forces. We distinguish between red-detuned and blue-detuned trapping, that is using a trapping wavelength shorter or longer than the plasmon resonance of the particle. So far optical trapping of metal nanoparticles has focussed on a wavelength regime far from the particle’s resonance in the infrared. We experiment with laser wavelengths close to the plasmon resonance and expand the knowledge of metal nanoparticle trapping available to date. Existing theoretical models are put to the test when we compare these with our real experimental situations.

The mammalian hippo signalling pathway controls cell proliferation and apoptosis via transcriptional co-activators YAP and TAZ, and as such is a key regulator of organ and tissue growth. Multiple cellular components converge in this pathway, including the actin cytoskeleton, which is required for YAP/TAZ activity. The precise mechanism by which the mechanical actomyosin network regulates Hippo signalling, however, is unknown. Optical methods provide a non-invasive way to image and study the biomechanics of cells. In the past two decades, super-resolution fluorescence microscopy techniques that break the diffraction limit of light have come to the fore, enabling visualisation of intracellular detail at the nanoscale level. Optical trapping, on the other hand, allows precise control of micron-sized objects such as cells. Here, super resolution structured illumination microscopy (SIM) and elastic resonator interference stress microscopy (ERISM) were used to investigate a potential role for the FERM-domain protein FRMD6, or Willin, in the mechanical control of the Hippo pathway in a neuronal cell model. A double optical trap was also integrated with the Nikon-SIM with the aim of cell stretching. Willin expression was shown to modify the morphology, neuronal differentiation, actin cytoskeleton and forces of SH-SY5Y cells. Optical trapping from above the SIM objective, however, was demonstrated to be ineffective for manipulation of adherent cells. The results presented here indicate a function for Willin in the assembly of actin stress fibres that may be the result of an interaction with the Hippo pathway regulator AMOT. Further investigation, for example by direct cell stretching, is required to elucidate the exact role of Willin in the mechanical control of YAP/TAZ.

Exploiter le degré de liberté angulaire de la lumière pour contrôler les forces optiques ouvre une nouvelle voie pour la manipulation optique de systèmes matériels. Dans ce contexte, notre travail porte sur l’interaction lumière-matière en présence de chiralité, qu’elle soit matérielle ou ondulatoire. Expérimentalement, nous avons utilisé des gouttes de cristaux liquides cholestériques interagissant avec un ou plusieurs champs lumineux polarisés circulairement et nous avons apporté une description quantitative de nos observations. Notre principal résultat correspond à la démonstration que la pression de radiation optique peut être contrôlée par l’hélicité du photon. Ce phénomène est ensuite utilisé, d’une part pour faire une démonstration de principe du tri de la chiralité matérielle via une approche optofluidique et d’autre part pour réaliser un piège optique tridimensionnel sensible à la chiralité de l’objet piégé. / Exploiting the angular momentum degree of freedom of light to control the mechanical effects that result from light-matter exchanges of linear momentum is an intriguing challenge that may open new routes towards enhanced optical manipulation of material systems. In this context, our work addresses the interplay between the chirality of matter and the chirality of optical fields. Experimentally, this is done by using cholesteric liquid crystal droplets interacting with circularly polarized light and we provide with theoretical developments to quantitatively support our observations. Our main result is the demonstration of optical radiation force controlled by the photon helicity. This phenomenon is then used to demonstrate the optofluidic sorting of material chirality and the helicity-dependent three-dimensional optical trapping of chiral liquid crystal microspheres.

Les nanocavités optiques sur puces sont devenues aujourd'hui des objets de base pour le piégeage et la manipulation d'objets colloïdaux. Nous étudions dans cette thèse des nanocavités comme briques de bases du piégeage et de la manipulation par forces optiques. La preuve de concept du piégeage de microsphères diélectriques apparaît comme le point de départ de l'élaboration d'un laboratoire sur puce. Dans le premier chapitre nous parcourons la bibliographie de l'utilisation des forces optiques en espace libre et en milieu confiné pour le piégeage de particules. Le second chapitre présente les dispositifs expérimentaux pour la caractérisation des nanocavités et les outils mis en place pour les mesures optiques en présence de particules colloïdales. Le troisième chapitre explique la preuve de concept du piégeage de particules de polystyrène de 500 nm, 1 et 2 µm. Dans le chapitre qui suit nous analysons le piégeage de particules en fonction de la puissance injectée dans la cavité. Le chapitre cinq décrit quelques exemples des possibilités de fonctions de manipulation de particules grâce à des cavités couplées. Enfin, dans le dernier chapitre nous montrons les assemblages de particules sur les différents types de cavités étudiées dans cette thèse. / On chips optical nanocavities have become useful tools for trapping and manipulation of colloidal objects. In this thesis we study the nanocavities as building blocks for optical forces, trapping and handling of particles. Proof of concept of trapping dielectric microspheres appears as the starting point of the development of lab on chip. In the first chapter we go through the literature of optical forces in free space and integrated optics. The second chapter presents the experimental tools for the characterization of nanocavities and the set-up developed to perform optical measurements with the colloidal particles. The third chapter describes the proof-of-concept trapping of polystyrene particles of 500 nm, 1 and 2 µm. In the following chapter we analyze the particle trapping as function of the injected power into the cavities. The chapter five gives some examples of the possibilities of particles handling functions with coupled cavities. Eventually, in the last chapter we show assemblies of particles on different geometry of cavities studied in this thesis.

Moving towards label-free technologies is essential for many clinical and research applications. Raman spectroscopy is a powerful tool in the field of biomedicine for label-free cell characterisation and disease diagnosis, owing to its high chemical specificity. However, Raman scattering is a relatively weak process and can require long acquisition times, thus hampering its integration to clinical technologies. Multimodal analysis is currently pushing the boundaries in biomedicine, obtaining more information than would be possible using a single mode and overcoming any limitations specific to a single technique. Digital holographic microscopy (DHM) is a rapid and label-free quantitative phase imaging modality, providing complementary information to Raman spectroscopy, and is thus an ideal candidate for combination in a multimodal system. Firstly, this thesis explores the use of wavelength modulated Raman spectroscopy (WMRS), for the classification of immune cell subsets. Following this a multimodal approach, combining Raman spectroscopy and DHM, is demonstrated, where each technique is considered individually and in combination. The complementary modalities provide a wealth of information (both chemical and morphological) for cell characterisation, which is a step towards achieving a label-free technology for the identification of human immune cells. The suitability of WMRS to discriminate between closely related neuronal cell types is also explored. Furthermore optical spectroscopic techniques are useful for the analysis of food and beverages. The use of Raman and fluorescence spectroscopy to successfully discriminate between various whisky and extra-virgin olive oil brands is demonstrated, which may aid the detection of counterfeit or adulterated samples. The use of a compact Raman device is utilised, demonstrating the potential for in-field analysis. Finally, monodisperse and highly spherical nanoparticles are synthesised. A short study demonstrates the potential for these nanoparticles to benefit the techniques of surface enhanced Raman spectroscopy and optical trapping, by way of minimising variability.

Les pinces optiques permettent de piéger et de manipuler des objets sans contact physique avec de la lumière et ce avec une extrême précision. Son caractère non-invasif et non-destructif en fait un outil idéal pour des applications dans des domaines tels que la biophysique et la médecine. La pince optique conventionnelle utilise un faisceau lumineux fortement focalisé par un objectif de microscope.La fibre optique est un composant très intéressant dans ce domaine puisqu'elle permet de guider la lumière et de piéger optiquement des objets sans l'utilisation de composants optiques encombrants et en limitant des étapes d'alignement. Elle donne ainsi une grande flexibilité et compacité aux pinces optiques.Dans ce contexte, l'objectif de cette thèse a été de développer une pince optique à deux fibres nano-structurées dans le but de piéger des particules de taille micro et nanométrique.Notre pince est constituée de deux fibres optiques gravées chimiquement en forme de pointe et positionnées en vis-à-vis à des distances typiques de 20 nm à 20 µm. Cette configuration à deux faisceaux contra-propagatifs permet d'annuler la pression de radiation de la lumière. Elle a l'avantage d'obtenir un piégeage efficace pour des intensités lumineuses relativement faibles. En outre, les faisceaux ne doivent pas nécessairement être fortement focalisés. Notre dispositif présente une grande souplesse grâce au contrôle in-situ de la position des fibres, l'injection de la lumière dans les fibres et la manipulation de particules individuelles sans aucun substrat.Au cours de ces travaux, nous avons démontré expérimentalement le piégeage stable et reproductible d'une ou plusieurs particules en suspension. Divers types de particules diélectriques ont été piégées, allant de la particule en polystyrène d'un micromètre à des particules luminescentes de YAG:Ce mesurant 60 nm de diamètre. Ces dernières ont été élaborées et optimisées spécifiquement pour le piégeage optique lors de ces travaux.Nous avons également mesuré les forces optiques appliquées aux particules piégées en analysant leur mouvement Brownien résiduel. Nous avons démontré que le potentiel de piégeage était harmonique, nous permettant de définir la constante de raideur optique.Enfin nous avons démontré qu'en modifiant la forme du faisceau optique d'émission, il était possible d'améliorer certaines caractéristiques de la pince. D'une part, les faisceaux quasi-Bessel qui sont très peu divergents nous ont permis de réaliser un piégeage stable et efficace à grande distance.D'autre part, l'utilisation de pointes métallisées permet de confiner le champ et d'améliorer les forces optiques tout en diminuant l'intensité lumineuse. Nous avons mis en évidence le couplage en champ proche entre deux pointes métallisées qui ont été spécialement élaborées pour la pince. Ces derniers résultats ouvrent des perspectives encourageantes pour le développement d'une pince plasmonique fonctionnant en champ proche qui est particulièrement bien adaptée pour le piégeage de nanoparticules. / Optical tweezers allow to trap and manipulate objects without any mechanical contact with light and with an extreme accuracy. This non-invasive and non-destructive technique is of large interest in many scientific domains such as biophysics and medicine. Conventional optical tweezers use a laser beam which is strongly focalised by a microscope objective.The use of optical fibers attracts increasing attention as highly flexible and compact tools for particle trapping. Fiber-based optical tweezers do not require bulky optics and require only little alignments.In this context, the objective of this thesis was to develop a dual fiber nano-tip optical tweezers in order to trap particles with micro and nano-meter sizes. Our tweezers consist of two chemically etched optical fiber tips placed in front of each other with typical gaps from 20~nm to 20~µm. This dual contra-propagative beams configuration allow to cancel light radiation pressure. Efficient trapping can thus be obtained at relative low light intensities. Moreover, strong focusing is not required. Our device present an high flexibility due to in situ optimization and control of the fibre positions and individual particle manipulation without any substrate.During our work, we experimentally demonstrated stable and reproducible trapping of one or several particles in suspension. Various dielectric particles were trapped, from one micrometer polystyrene beads to luminescent YAG:Ce particles with diameters down to 60~nm. During this thesis, the latter were specifically elaborated and optimized for the optical trapping. We also measured optical forces applied to trapped particles by analysing their residual Brownian motion. We showed the trapping potential is of harmonic shape, allowing to define its optical stiffness.vspace{10pt}Finally, by modifying the emitted optical beam shape, we were able to improve specific tweezers characteristics. On one hand, nondiffracting quasi-Bessel beams allow us to get a stable trapping at large fiber-to-fiber distances.On the other hand, the use of metallised fiber tips allows to improve the beam confinement and enhance optical forces while reducing light intensity. We proved the near-field coupling between two metallised tips which were especially elaborated in this work. Those last results open promising perspectives for the development of plasmonic tweezers working in the near-field, which are especially well adapted for nano-particles trapping.