Surface plasmon is the quantized collective oscillation of the free electron gas in a metallic material. By coupling surface plasmons with photons in different nanostructures, researchers have found surface plasmon polaritons (SPP) and localized surface plasmon resonance (LSPR), which are widely adopted in biosensing, single molecule sensing and detection via surface enhanced raman scattering (SERS), photothermal ablation treatments for cancer, optical tagging and detection, strain sensing, metamaterials, and other applications. The overall objective of this dissertation is to investigate both how mechanics impacts the optical properties, and also how optics impacts the mechanical properties of metal nanostructures reversely. Mechanically engineering individual nanostructures(forward coupling) offers the freedom to alter the optical properties with more flexibility and tunability. It is shown that elastic strain can be applied to gold nanowires to reduce the intrinsic losses for subwavelength optical signal processing, leading to an increase of up to 70% in the surface plasmon polariton propagation lengths at resonance frequencies. Apart from strain engineering, defects are another important aspect of mechanically engineering nanoscale materials, whose impacts on the optical properties of metal nanostructures remain unresolved. An atomic electrodynamic model has been derived to demonstrate that those effects are crucial for ultrasmall nanoparticles with characteristic sizes around 2 nm, and can be safely ignored for those larger than about 5 nm due to the important contribution of nanoscale surface effects. Another key focus of this research project (reverse coupling) is to investigate the currently unknown effects that an external optical field has on the mechanical properties of metal nanostructures. Since each atom in the nanostructure acts as a dipole due to induced electron motions, this optical excitation introduces additional dipolar forces that add to the standard mechanical atomic interactions, which could alter the mechanical properties of the nanostructures. Furthermore, it is shown that when linking mechanics with LSPR, because the metal is dispersive, the mechanical behavior or the strength of the nanostructure should be dependent on the frequency of the electromagnetic excitation. To study this phenomenon, a simpler case with an electrostatic field excitation is considered first, and conclusions are reached on how static fields can be used to tune the elasticity of metallic nanostructures with different sizes and axial orientations and surfaces. Then building upon those understandings, studies were carried out in determining the effects of an optical field, specifically at LSPR frequency, on the mechanical properties of metallic nanostructures. It is found that the initial relaxation strain induced by the static field or optical field is the key factor leading to the variations in the stiffness of the metallic nanostructures that are excited by optical fields at the LSPR frequencies.

Les systèmes optomécaniques, dans lesquels les vibrations d'un résonateur mécanique sont couplées à un rayonnement électromagnétique, ont permis l'examen de multiples nouveaux effets physiques. Afin d'exploiter pleinement ces phénomènes dans des circuits réalistes et d'obtenir différentes fonctionnalités sur une seule puce, l'intégration des résonateurs optomécaniques est obligatoire. Ici nous proposons une nouvelle approche pour la réalisation de systèmes intégrés et hétérogènes comportant des cavités à cristaux photoniques bidimensionnels au-dessus de guides d'ondes en silicium-sur-isolant. La réponse optomécanique de ces dispositifs est étudiée et atteste d'un couplage optomécanique impliquant à la fois les mécanismes dispersifs et dissipatifs. En contrôlant le couplage optique entre le guide d'onde intégré et le cristal photonique, nous avons pu varier et comprendre la contribution relative de ces couplages. Cette plateforme évolutive permet un contrôle sans précédent sur les mécanismes de couplage optomécanique, avec un avantage potentiel dans des expériences de refroidissement et pour le développement de circuits optomécaniques multi-éléments pour des applications tels que le traitement du signal par effets optomécaniques. / Optomechanical systems, in which the vibrations of a mechanical resonator are coupled to an electromagnetic radiation, have permitted the investigation of a wealth of novel physical effects. To fully exploit these phenomena in realistic circuits and to achieve different functionalities on a single chip, the integration of optomechanical resonators is mandatory. Here, we propose a novel approach to heterogeneously integrated arrays of two-dimensional photonic crystal defect cavities on top of silicon-on-insulator waveguides. The optomechanical response of these devices is investigated and evidences an optomechanical coupling involving both dispersive and dissipative mechanisms. By controlling optical coupling between the waveguide and the photonic crystal, we were able to vary and understand the relative strength of these couplings. This scalable platform allows for unprecedented control on the optomechanical coupling mechanisms, with a potential benefit in cooling experiments, and for the development of multi-element optomechanical circuits in the frame of optomechanically-driven signal-processing applications.

The topic of this thesis is the theoretical analysis of theoptomechanical coupling effects in a high-finesse optical cavity, and the experimental realization of such a device.Radiation pressure exerted by light limits the sensitivity of high precision optical measurements. In particular, the sensitivity of interferometric measurements of gravitational wave is limited by the so called standard quantum limit. cavity with a movable mirror. The internal field stored in such cavity can be orders of magnitude greater than the input field, and it's radiation pressure force can change the physical length of the cavity. In turn, any change in the mirror's position changes the phase of the out put field. This optomechanical coupling leads to an intensity-dependent phase shift for thelight equivalent to an optical Kerr effect. Such a device can then be used for squeezing generation or quantum nondemolition measurements.In our experiment, we send a laser beam in to a high-finesse optical cavity with a movable mirror coated on a high Q-factor mechanical resonator. Quantum effects of radiation pressure become therefore, at low temperature, experimentally observable. However, we've shown that the phase of the reflected field is very sensitive to small mirror displacements, which indicate other possible applications of thistype of device like high precision displacements measurements. We've been able to observe the Brownian motion of the moving mirror. We've also used an auxiliary intensity modulated laser beam to optically excite the acoustic modes. We've finally obtained a sensitivity of2x10^(-19) m/sqrt(Hz), in agreement with theoretical prediction.