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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Spin Optomechanics of Levitated Nanoparticles

Jonghoon Ahn (9127940) 05 August 2020 (has links)
With the unique advantage of great isolation from the thermal environment, levitated optomechanics has emerged as a powerful platform for various fields of physics including microscopic thermodynamics, precision measurements, and quantum mechanics. Experiments with optically levitated micro- and nanoparticles have already obtained remarkable feats of zeptonewton force sensing and ground-state cooling. The novel system has also been proposed to assess various theories including the objective collapse models and macroscopic quantum mechanics. <br><div><br></div><div>This thesis reports experimental results on a levitated Cavendish torsion balance, a GHz nanomechanical rotor, and a torque sensor with unprecedented sensitivity realized with optically levitated nanoparticles in a vacuum environment. The system at room temperature achieves a sensitivity of (4.2±1.2)×10−27Nm/ √ Hz surpassing the sensitivity of most advanced nanofabricated torque sensors at cryogenic environments. Calculations suggest potential detection of Casimir torque and vacuum friction under realistic conditions. Moreover, the nanoparticles are driven into ultrafast rotations exceeding 5 GHz, which achieves the fastest humanmade nanomechanical rotor. Such fast rotations allow studies on the ultimate tensile strength of the nanoparticles as well. <br></div><div><br></div><div>Subsequently, the electron spin control of nitrogen vacancies (NV) in optically trapped diamond naoparticles is demonstrated in low vacuum. The configuration is analogous to trapped atoms and ions which serve as a quantum system with internal states. The effect of the air pressure, surrounding gas, and laser power on the electron spin resonance (ESR) are studied, and the temperature of the diamond is also measured with the ESR. The levitated nanodiamonds will provide the means to implement a hybrid spin-optomechanical system.<br></div>
2

Effets mécaniques de la lumière sur des particules anisotropes micrométriques et dynamique du mouillage à l’interface eau-air / (Mechanical effects of light on anisotropic micron-sized particles and their wetting dynamics at the water-air interface

Mihiretie, Besira 05 July 2013 (has links)
Nous présentons une série d’expériences sur des particules micrométriques de polystyrène de formes ellipsoïdales. Les rapports d’aspects (k) des particules sont variables, de 0.2 à 8 environ. Ces ellipsoïdes sont manipulés dans l’eau par faisceau laser modérément focalisé. On observe la lévitation et l’équilibre dynamique de chaque particule, dans le volume et au contact d’une interface, solide-liquide ou liquide-liquide. Dans une première partie, nous montrons que des particules de k modéré sont piégées radialement. Par contre, les ellipsoïdes allongés (k>3) ou aplatis (k<0.3) ne peuvent pas être immobilisés. Ces particules « dansent » autour du faisceau, dans un mouvement permanent associant translation et rotation. Les mouvements sont périodiques, ou irréguliers (chaotiques) selon les caractéristiques de la particule et du faisceau. Un modèle en 2d est proposé qui permet de comprendre l’origine des oscillations. La seconde partie est une application de la lévitation optique pour une étude de la transition mouillage total-mouillage partiel des particules à l’interface eau-air. Nous montrons que la dynamique de la transition ne dépend pratiquement pas de la forme de particule, et qu’elle est déterminée par le mécanisme d’accrochage-décrochage de la ligne de contact. / We report experiments on ellipsoidal micrometre-sized polystyrene particles. The particle aspect ratio (k) varies between about 0.2 and 8. These particles are manipulated in water by means of a moderately focused laser beam. We observe the levitation and the dynamical state of each particle in the laser beam, in bulk water or in contact to an interface (water-glass, water-air, water-oil). In the first part, we show that moderate-k particles are radially trapped with their long axis lying parallel to the beam. Conversely, elongated (k>3) or flattened (k<0.3) ellipsoids never come to rest, and permanently “dance” around the beam, through coupled translation-rotation motions. The dynamics are periodic or irregular (akin to chaos) depending on the particle type and beam characteristics. We propose a 2d model that indeed predicts the bifurcation between static and oscillating states. In the second part, we apply optical levitation to study the transition from total to partial wetting of the particles at the water-air interface. We show that the dynamics of the transition is about independent of particle shape, and mainly governed by the pinning-depinning mechanism of the contact line.
3

Behaviour of Objects in Structured Light Fields and Low Pressures / Behaviour of Objects in Structured Light Fields and Low Pressures

Flajšmanová, Jana January 2021 (has links)
Studium chování opticky zachycených částic nám umožňuje porozumět základním fyzikálním jevům plynoucím z interakce světla a hmoty. Předkládaná práce podává vysvětlení zesílení tažné síly působící na opticky svázané částice ve strukturovaném světelném poli, tzv. tažném svazku. Ukazujeme, že pohyb dvou opticky svázaných objektů v tažném svazku je silně závislý na jejich vzájemné vzdálenosti a prostorové orientaci, což rozšiřuje možnosti manipulace hmoty pomocí světla. Následně se práce zaměřuje na levitaci opticky zachycených částic ve vakuu. Představujeme novou metodologii na charakterizaci vlastností slabě nelinearního Duffingova oscilátoru reprezentovaného opticky levitující částicí. Metoda je založena na průměrování trajektorií s určitou počáteční pozicí ve fázovém prostoru sestávajícím z polohy a rychlosti částice a poskytuje informaci o parametrech oscilátoru přímo ze zaznamenaného pohybu. Náš inovativní postup je srovnán s běžně užívanou metodou založenou na analýze spektrální hustoty polohy částice a za využití numerických simulací ukazujeme její použitelnost i v nízkých tlacích, kde nelinearita hraje významnou roli.

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