Aside from energy, light carries linear and angular momenta that can be transferred to matter. The interaction between light and matter is governed by conservation laws that can manifest themselves as mechanical effects acting on both matter and light waves. This interaction permits remote, precise, and noninvasive manipulation and sensing at microscopic levels. In this dissertation, we demonstrated for the first time a complete set of opto-mechanical effects that are based on nonconservative forces and act at the interface between dielectric media. Without structuring the light field, forward action is provided by the conventional radiation pressure while a backward movement can be achieved through the natural enhancement of linear momentum. If the symmetry of scattered field is broken, a side motion can also be induced due to the transformation between spin and orbital angular momenta. In experiments, these opto-mechanical effects can be significantly amplified by the long-range hydrodynamic interactions that provide an efficient recycling of energy. These unusual opto-mechanical effects open new possibilities for efficient manipulation of colloidal microparticles without having to rely on intricate structuring or shaping of light beams. Optically-controlled transport of matter is sought after in diverse applications in biology, colloidal physics, chemistry, condensed matter and others. Another consequence of light-matter interaction is the modification of the optical field itself, which can manifest, for instance, as detectable shifts of the centroids of optical beams during reflection and refraction. The spin-Hall effect of light (SHEL) is one type of such beam shifts that is due to the spin-orbit transformation governed by the conservation of angular momentum. We have shown that this effect can be amplified by the structural anisotropy of random nanocomposite materials.

abstract: This thesis explores the potential application of the phase change material tungsten trioxide (WO3) in optical force modulation for spacecraft and satellites. It starts with a literature review of past space optical force applications as well as potential phase change materials for optical force modulation. This is followed by the theoretical model and discussions of the optical properties of a variety of materials used in the structures explored thereafter. Four planar structures were analyzed in detail. Two of the structures were opaque and the other two were semi-transparent. The first of the opaque structures was a tungsten trioxide film on aluminum substrate (WO3/Al). It was found to have a 26% relative change in radiation pressure with WO3 thickness of 200 nm. The second opaque structure was a tungsten trioxide film on silicon spacer on aluminum substrate (WO3/Si/Al). This structure was found to have a 25% relative change in radiation pressure with 180 nm WO3 and 20 nm Si. The semitransparent structures were tungsten trioxide film on undoped silicone substrate (WO3/Si), and a tungsten trioxide film on a silicone spacer on tungsten trioxide (WO3/Si/WO3). The WO3/Si structure was found to have an 8% relative change in radiation pressure with 200 nm WO3 and 50 nm Si. The WO3/Si/WO3 structure had a relative change in radiation pressure of 20% with 85 nm WO3 and 90 nm Si. These structures show promise for attitude control in future solar sailing space missions. The IKAROS mission proved the functionality of using phase change material in order to steer a space craft. This was accomplished with a 7.8% relative change in radiation pressure. However, this only occurred at a pressure change of 0.11 µN/m2 over a range of 0.4 to 1.0 µm which is approximately 77.1% of the solar spectrum energy. The proposed structure (WO3/Al) with a 26% relative change in radiation pressure with a pressure change of 1.4 µN/m2 over a range 0.4 to 1.6 µm which is approximately 80% of the solar spectrum energy. The magnitude of radiation pressure variation in this study exceeds that used on the IKAROS, showing applicability for future mission. / Dissertation/Thesis / Masters Thesis Aerospace Engineering 2020

Le travail réalisé dans cette thèse porte sur l’étude du mouvement Brownien d’une suspension colloïdale sous champ de force optique faible et l’étude fondamentale des effets convectifs et de diffusion anormale. Nous avons construit un microscope à fond noir afin de suivre les particules et de reconstruire leurs trajectoires avec une résolution spatiale de 20 nm et une résolution temporelle de 8 ms. Ces trajectoires sont analysées statistiquement afin d’en extraire la contribution balistique induite par la force de pression de radiation appliquée par le laser d’illumination. En plus de l’effet mécanique du laser sur les particules, le fluide absorbe les radiations ce qui le chauffe et crée ainsi une différence de température entre la partie illuminée et la partie non illuminée de l’échantillon.Nous validons aussi les hypothèses de stationnarité et d’érgodicité qui sont fondamentales pour notre stratégie de mesure de force faible. L’analyse statistique fine de notre système nous permet de mettre en évidence et de caractériser des effets de diffusion anormale brownienne. Nos expériences révèlent en effet la présence de trajectoires anormales dont l’origine se comprend comme un effet d’interaction entre la particule suivie et le reste de l’ensemble colloïdal. / The work presented in this thesis deals with the study of the Brownian motion of a colloidal suspension under an external weak optical force, the study of convective effects and anomalous diffusion. We have built a dark field microscope in order to track the particles and reconstruct the Brownian trajectories with a spatial resolution of 20 nm and a temporal resolution of 8 ms.Statistical analysis of the trajectories has allowed us to extract the ballistic contribution induced by the radiation pressure force exerted by irradiating a laser on the particles. In addition to the mechanical effect of the laser on the particles, the fluid absorbs the radiation. Consequently, the temperature of the fluid rises and results in a thermal difference between the illuminated and the non-illuminated areas of the sample. In order to validate our weak force measurement, we have investigated two fundamental hypotheses in statistical physics: ergodicity and stationary aspect. A closer statistical analysis enables us to demonstrate and characterize the effect of anomalous Brownian diffusion. Our experiments have revealed the existence of anomalous trajectories, which can be understood as an effect of the interactions between the particles.

The recent demonstration of strong interactions between optical force and mechanical motion of an optomechanical structure has led to the triumphant result of mechanical ground-state cooling, where the quantum nature of a macroscopic object is revealed. Another intriguing demonstration of quantum physics on a macroscopic level is the measurement of the Casimir force which is a manifestation of the zero- point energy. An interesting aspect of the Casimir effect is that the anharmonicity of the Casimir potential becomes significant when the separation of microscale objects is in the sub-100nm regime. This regime is readily accessible by many of the realized gradient-force-based optomechanical structures. Hence, a new avenue of probing the Casimir effect on-chip all-optically has become available. We propose an integrated optomechanical platform, consisting of a suspended photonic crystal membrane evanescently coupled with a silicon-on-insulator substrate, for (i) measuring the Casimir force gradient and (ii) counteracting the attractive force by exerting a resonantly enhanced repulsive optical gradient force. This thesis first presents the full characterization of the optomechanical properties of the system in vacuo. The interplay of the optical gradient force (optomechanical coupling strength \(g_{om}/2\pi=- 66GHz/nm\)) and the photothermal force manifested in the optical spring effect and dynamic backaction is elucidated. Static displacement by the repulsive force of 1nm/mW is also demonstrated. In the second part of the thesis, the nonlinear mechanical signatures upon a strong coherent drive are reported. By resonantly driving the photonic crystal membrane with a piezo-actuator and an optical gradient force, we observed mechanical frequency mixing, mechanical bistability and non-trivial interactions of the Brownian peak with the driving signal. Finally we present our recent progress in establishing electro- static control of individual photonic crystal membranes to reduce and calibrate the electrostatic artifact which plagues Casimir measurements. The results discussed in this thesis point towards an auspicious future of a complete realization of a Casimir optomechanical structure and novel applications with nonlinearity afforded by the Casimir force and the optical gradient force. / Engineering and Applied Sciences

Understanding microscale biological processes as cells develop into tissues is one of the most important, yet most difficult, problems in modern biology. Cells encounter a dynamic chemical and physical environment and delineating the myriad of variables proves daunting with even the most sophisticated experiments. This dissertation focuses on the development and application of unique enabling technologies designed to sample and control biological microenvironments. By developing two approaches – one aimed at intracellular biochemistry and another for extracellular targets – based on photochemistry and optical force generation, research presented here will allow new areas of subcellular dynamics to be addressed. On the intracellular side, enzyme-immobilized polymeric microspheres or enzyme microstructures are placed into the cell cytosol via optical tweezers for sustained and localized chemical modification of the intracellular environment. This approach is complemented by the use of extracellular guidance barriers formed from photo-induced crosslinking of proteins. Through the use of minimally toxic photosensitizers and femtosecond (fs) near infrared (NIR) light, it is possible to fabricate three-dimensional protein structures in a living cell’s environment. Moreover, this work explores the ability to form protein structures with enzymatic activity as well as with high aspect-ratio features at micron resolution. Finally, the photochemical transformation of serotonin into a highly fluorescent visible photoproduct is investigated as a means to overcome problems associated with sample size in neurotransmitter detection during synaptic chemical signaling. Optimization of this multiphoton process entails understanding the mechanism by which the photoproduct is created and experiments towards this goal are presented here. Ultimately, the precision and flexibility of these technologies will allow access to new areas of the biosciences. / text

To respond to rapidly-changing stresses in their environment, bacterial cells must be able to sense a variety of chemical cues and respond to them by activating the relevant genes. The lysine riboswitch is a short RNA motif, located just upstream of a gene encoding a lysine biosynthesis protein, that suppresses the expression of that gene when sufficient lysine is present in the cell. It acts by binding a lysine monomer in a region called the aptamer, which in turn rearranges an adjacent domain called the expression platform, sequestering the ‘start' sequence of the gene and preventing it from being transcribed. In this thesis, the lysine riboswitch's ligand-binding transition is studied using single-molecule fluorescence microscopy, optical tweezers, and a hybrid optical force/fluorescence technique. Förster Resonance Energy Transfer (FRET) is used with a fluorescently-labeled aptamer to show that it has a previously-undescribed, partially-folded structural state with enhanced ligand affinity compared to the unfolded structure. The Mg²⁺ dependence of the transition between these states is shown to resolve existing debates in the literature about the sensitivity of the riboswitch. The kinetics of the folding transition are explored using FRET, optical force, and hybrid ‘Fleezers' to map the free energy landscape of ligand binding and show that the ligand itself promotes transitions into the aptamer's folded state, a so-called ‘induced fit' mechanism rare among riboswitches. Finally, high-resolution optical tweezers are used to explore the link between the aptamer's secondary structure (the sequence of paired nucleotides) and its tertiary structure (three-dimensional folding) to illuminate the role of ligand binding in gene regulation, which depends on the equilibrium between competing secondary structures. Hybrid biophysical techniques like optical force/fluorescence microscopy are shown to be indispensable for addressing all the states in the reaction pathways of complex biomolecules like riboswitches and for discriminating between multiple levels of structure formation and interaction with the environment. Not only do the results presented here shed light on the RNA folding problem, particularly the role of tertiary structure in determining the minimum-energy configuration of an RNA sequence, but they could have implications for biomedical research, as the lysine riboswitch has already been shown to be a potential target for next-generation antibiotics.

abstract: This research focuses mainly on employing tunable materials to achieve dynamic radiative properties for spacecraft and building thermal management. A secondary objective is to investigate tunable materials for optical propulsion applications. The primary material investigated is vanadium dioxide (VO2), which is a thermochromic material with an insulator-to-metal phase transition. VO2 typically undergoes a dramatic shift in optical properties at T = 341 K, which can be reduced through a variety of techniques to a temperature more suitable for thermal control applications. A VO2-based Fabry-Perot variable emitter is designed, fabricated, characterized, and experimentally demonstrated. The designed emitter has high emissivity when the radiating surface temperature is above 345 K and low emissivity when the temperature is less than 341 K. A uniaxial transfer matrix method and Bruggeman effective medium theory are both introduced to model the anisotropic properties of the VO2 to facilitate the design of multilayer VO2-based devices. A new furnace oxidation process is developed for fabricating high quality VO2 and the resulting thin films undergo comprehensive material and optical characterizations. The corresponding measurement platform is developed to measure the temperature-dependent transmittance and reflectance of the fabricated Fabry-Perot samples. The variable heat rejection of the fabricated samples is demonstrated via bell jar and cryothermal vacuum calorimetry measurements. Thermal modeling of a spacecraft equipped with variable emittance radiators is also conducted to elucidate the requirements and the impact for thermochromic variable emittance technology. The potential of VO2 to be used as an optical force modulating device is also investigated for spacecraft micropropulsion. The preliminary design considers a Fabry-Perot cavity with an anti-reflection coating which switches between an absorptive “off” state (for insulating VO2) and a reflective “on” state (for metallic VO2), thereby modulating the incident solar radiation pressure. The visible and near-infrared optical properties of the fabricated vanadium dioxide are examined to determine if there is a sufficient optical property shift in those regimes for a tunable device. / Dissertation/Thesis / Doctoral Dissertation Aerospace Engineering 2020

<div>Aperiodic structures offer new functionalities for control, manipulation, and sensing that can benefit applications in all frequency ranges. We present a study of the influence of the degrees of freedom from a binary aperiodic nanostructure in free space, where each pixel is either the scatterer or the background, that uses a multivariate statistical analysis to examine the covariance matrix of the output field distributions. The total variance of the output fields and the rank can be evaluated to provide quantitative measurements of control. In addition, the field statistics provide an improved understanding of the scattering properties of aperiodic structures.</div><div><br></div><div><br></div><div><div>It has been proposed that structuring a metal surface can substantially increase the optical pressure over that possible with a planar interface. Based upon the forces on the mirrors of a one-dimensional asymmetric Fabry-Perot cavity, we show that the sum of the pressures on both mirrors increases through asymmetry and with quality factor. Using cavity quality factor as a measure, we present the physical basis of the enhanced pressure on a nanostructured metallic surface as being due to an array of asymmetric resonant cavities.</div></div><div><br></div><div><div>With use of optimized, aperiodic structures, more control and higher pressure should be possible. We present a design method by which the electromagnetic pressure on a nanostructured binary material can be controlled in terms of both the enhancement and the direction. This analysis offers new avenues for optomechanics.</div></div>

No description available.

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.