Light can exert optical forces on matter. In the macroscopic world these forces are minuscule, but on the microscopic or atomic scale, these forces are large enough to trap and manipulate particles. They may even be used to cool atoms to a fraction of a degree above absolute zero. \n \nThis thesis details a number of experiments concerned with the optical manipulation of atoms and micron-size particles using free space light beams and photonic crystal fibres. \n \nTwo atom guiding experiments are described. In the first experiment, a spatial light modulator is used to generate higher blue-detuned azimuthal Laguerre-Gaussian LG) beams, which are annular beams with a hollow core. These LG beams are then used to guide laser cooled rubidium-85 atoms within the dark core over a distance of 30 mm. The second atom guiding experiment involves attempting to guide laser cooled and thermal rubidium atoms through a hollow-core photonic crystal fibre using red-detuned light. Hollow-core photonic crystal fibres are fibres that are able to guide light with low attenuation within a hollow core. For this experiment a hot wire detection system was designed, along with a number of complex vacuum systems. \n \nThe first dual-beam fibre trap for micron-size particles constructed using endlessly single-mode photonic crystal fibre (ESM-PCF) is described. The characteristics of dual-beam fibre traps are governed by the fibres used. As ESM-PCF has considerably different properties in comparison to conventional single- or multimode fibres, this dual beam ESM-PCF trap exhibits some novel characteristics. I show that the dual beam ESM-PCF trap can form trapping, repulsive and line potentials; an interference-free ‘white light’ trap; and a dual-wavelength optical conveyor belt.
Light can exert optical forces on matter. In the macroscopic world these forces are minuscule, but on the microscopic or atomic scale, these forces are large enough to trap and manipulate particles. They may even be used to cool atoms to a fraction of a degree above absolute zero. \n \nThis thesis details a number of experiments concerned with the optical manipulation of atoms and micron-size particles using free space light beams and photonic crystal fibres. \n \nTwo atom guiding experiments are described. In the first experiment, a spatial light modulator is used to generate higher blue-detuned azimuthal Laguerre-Gaussian LG) beams, which are annular beams with a hollow core. These LG beams are then used to guide laser cooled rubidium-85 atoms within the dark core over a distance of 30 mm. The second atom guiding experiment involves attempting to guide laser cooled and thermal rubidium atoms through a hollow-core photonic crystal fibre using red-detuned light. Hollow-core photonic crystal fibres are fibres that are able to guide light with low attenuation within a hollow core. For this experiment a hot wire detection system was designed, along with a number of complex vacuum systems. \n \nThe first dual-beam fibre trap for micron-size particles constructed using endlessly single-mode photonic crystal fibre (ESM-PCF) is described. The characteristics of dual-beam fibre traps are governed by the fibres used. As ESM-PCF has considerably different properties in comparison to conventional single- or multimode fibres, this dual beam ESM-PCF trap exhibits some novel characteristics. I show that the dual beam ESM-PCF trap can form trapping, repulsive and line potentials; an interference-free ‘white light’ trap; and a dual-wavelength optical conveyor belt.
In this thesis I describe experimental work and present data on the guiding of \nRubidium atoms along free-space propagating light beams as well as within hollow \ncore glass fibres, namely photonic crystal fibres. I describe experiments, laser systems \nand vacuum trap assemblies designed to facilitate this guiding. \nThese experiments are intended to aid progression within the field of cold \natom guidance wherein narrow diameter, long distance hollow-fibre guides are a \ncurrent goal. Realisation of these guides could lead to promising applications such as \natom interferometers and spatially accurate, multi-source, atom depositors. \nHerein, guided fluxes are observed in free-space guiding experiments for \ndistances up to 50mm and up to 10GHz red-detuning from resonance. Additionally \nhollow-core, Kagome structured, quasi- and true-photonic crystal fibres are \ncharacterised. Finally a number of detailed fibre-guiding magneto-optic traps are \ndeveloped. \nBoth cold atomic-beams and cold atomic clouds are reliably positioned above \nfibre entrance facets in conjunction with a guiding laser beam coupled into the fibre \ncore. \nIssues regarding optical flux detection outwith fibre confinement appear to \nhave hindered observation of guided atoms. A far more sensitive detection system has \nbeen developed for use in current, ongoing fibre-guide experiments.
This thesis is concerned with the guiding of cold atoms using optical forces, which is of great importance in the field of atom optics. Atomic beams can be used for precision sensor equipment, building nano-scale structures, construction of quantum computers and to further the understanding of the properties of atoms. Atoms are guided along light beams using the dipole force; there are two regimes under which this force works. Typically red-detuned guides are used (atoms are attracted towards the light) such guides, however, require large detuning and high powers. In this thesis we investigate the use of blue-detuned (atoms are repelled from the light) hollow light beams of moderate power (a few hundred mW) and confine atoms in the dark centre of the beams. Several magneto-optical traps (MOTs) have been constructed to exploit different guiding geometries. Hollow beams have been generated using a variety of methods; in particular the use of a computer controlled spatial light modulator (SLM) has provided great versatility and simplicity to the experimental arrangements. First, experiments were performed with a low-velocity intense source (LVIS) of atoms. A co-linear LG beam significantly enhances the observed flux, however, considerable difficulties are encountered loading atoms into oblique guides. Imaging a hole in the walls of the light tube was used to improve the loading efficiency. Second, guiding a free-falling atom cloud is performed using a non-diffracting Bessel beam. It is found that while the potential of the Bessel beam is steeper than equivalent LG beams the power distribution across the beam severely limits its usefulness. The next study investigated higher-order LG guide beams generated with an SLM. High order modes have a narrower profile so confine the atoms with less interaction with the guide beam, leading to a more natural guide (as opposed to a pushing force). Finally the SLM was used to create non-trivial beam shapes for beam splitters and interferometers.
This thesis reports on the design and fabrication of an experimental platform for in-fibre laser cooling of Rb and atom optics. By in-fibre laser cooling, we mean the long term aim of laser cooling thermal Rb atoms of a Photonic MicroCell (PMC), and subsequently developing what would be cold-atom photonic crystal fibre (PCF). The platform was designed to harbor several experiments on cold and thermal atom guidance and in-fibre spectroscopy so to address several open questions related for example to the effect of the core inner-wall surface on the atom energy structure and on selective fibre mode excitation for atom trapping and cooling. The completed platform comprises a specific and large ultra-high vacuum (UHV) chamber and a set of lasers for both atom cooling and atom guiding inside highly tailored hollow-core PCF (HC-PCF). The UHV chamber was designed to accommodate several HC-PCFs and two magneto-optical traps (MOT). The HC-PCF were designed, fabricated and post-processed to exhibit different core diameter, modal content and core inner surface material. For example, the mode field diameters range from ~30 µm to ~80 µm for the fundamental Gaussian-like core mode, and the surface materials include pure silica, a layer of Aluminosilicate or a layer of PDMS so to provide a large parameter space in assessing the effect of surface on the fibre-confined atoms. The system has been constructed and characterized. The cooling/repumping laser was frequency-stabilized, with measured Allan variance deviation of σ(τ)=3.8×10^(-11)/√τ. With the system we generated MOT with both isotopes of the Rb atom, with a cooling temperature as low as 7 µK. The platform is now operational to undertake the first atom guidance and explore the feasibility of atom cooling inside a HC-PCF.
Summary form only given. Recent advances in cold atom physics have seen the emergence of the area of atom guiding along hollow core optical fibres and also along light beams. Both employ the optical dipole force which for suitably tuned light can restrict the atoms to the dark hollow region of the fibre or the light beam. In this work, we discuss and analyse a novel scheme of channelling cold atoms into a high-order Bessel beam (via a high-order Laguerre-Gaussian beam) and demonstrate an efficient method of producing such beams.
Cette these decrit les progres et techniques realisees pour obtenir un couplage efficace d'atomes froids 85Rb dans une fibre optique en cristaux photonique a coeur vide et utilisant un guidage atomique a l'aide d'un faisceau laser creux de premier ordre decale en frequence vers le bleu. Dans le systeme propose, la faible diffraction de ce faisceau de premier ordre lui permet d'agir comme un entonnoir optique a potentiel repulsif servant a guider les atomes froids,avec l'aide de la gravite, dans le coeur de la fibre optique. L'utilisation d'une fibre optique a
faible perte, plutot qu'un capillaire permet de developper le potentiel de guider les atomes sur une trajectoire arbitraire et des distances a l'echelle du laboratoire. Ceci permettrait ainsi plusieurs nouvelles applications en nanofabrication et en metrologie optique.
Pour realiser cet objectif, un piege Magneto-Optique de 85Rb a ete bâtit de zero et en utilisant les techniques les plus avancees de refroidissement laser par gradient de polarisation a permis d'atteindre regulierement des temperatures de 9K dans une melasse optique contenant
10 7 atomes. Ces atomes froids furent guides au-dela de 23 cm dans un faisceau creux collime et decale vers le bleu et au travers de ce faisceau focalise de maniere a reproduire les conditions d'entree dans une fibre optique tout en permettant une observation precise des dynamiques de couplage. Trois classes d'atomes furent observees : perdus, pieges et guides. Les dynamiques de ce systeme ainsi que les conditions optimales de couplage ont ete identifies grâce au modele physique numerique ayant ete developpee.
Une nouvelle approche au probleme de la modelisation de la dynamique des atomes froids dans l'entonnoir optique a ete developpee au cours de cette these. Ce nouveau modele a
permis de reproduire la dynamique des atomes observes dans l'experience mais a aussi pu etre applique dans la simulation d'atomes froids dans le piege Magneto-Optique et a la prediction des temperatures atteintes dans diverses conditions experimentales. Ceci a ete realise grâce a
la modelisation 3D des composantes conservatives and non-conservatives des forces optiques agissant sur les atomes. L'implementation des mecanismes d'echauffement connu des atomes :la diffusion de lumiere et de leur quantite de mouvement, fut aussi cruciale a cette fin. Ce modele nous a aide a identifier les meilleures conditions de couplage dans ce systeme,corrobore par l'experience, et qu'il existait un potentiel optique optimal, pour une distance de couplage determine, qu'il ne fallait pas depasser.
Un faisceau LG01, monomode et de haute purete fut genere avec une efficacite superieure a 50% en utilisant un hologramme a valeurs complexes genere par ordinateur et rendu grâce a un modulateur de phase spatiale a base de cristaux liquides.----------Abstract This thesis describes advances and techniques toward the efficient coupling of cold 85Rb atoms into a low loss hollow core photonic crystal fibre using a blue-detuned first order hollow beam. In the proposed system, the low diffraction of the blue-detuned first order hollow beam acts as a repulsive potential optical funnel that allows the coupling of cold atoms under the influence of gravity into the fibre's hollow core. Using a low loss fibre with a blue detuned hollow beam shows potential for guiding atoms over an arbitrary path and longer distances on the laboratory scale, which would enable several new applications in nanofabrication and optical metrology.
To realize this objective, a Magneto-Optical Trap of 85Rb was built from scratch and by using advanced polarization gradient cooling techniques was turned into a 9 K cold optical molasses containing 107 atoms. These cold atoms were guided over 23 cm in a collimated blue detuned hollow beam tunnel and through a focused hollow beam mimicking as closely as possible the coupling conditions for a hollow core optical fibre. Three classes of atoms were observed: lost, trapped and guided atoms. The dynamics of the system as well as the optimal coupling conditions were identifed through the use of a numerical model. A novel approach to modelling cold atom dynamics in an optical funnel was developed during the course of this thesis. This new model was not only able to reproduce the dynamics of atoms in the experiment but also simulate dense cold atoms cooled into the MOT and predict final temperatures attained. This was achieved by 3D modelling of the conservative and non-conservative components of optical forces acting on atoms but also through the implementation of known heat mechanisms: light scattering and momentum diffusion. The
model identifed the best coupling conditions of this system, confirmed by experiment, and an optimal light potential for a given distance of coupling that must not be exceeded. A single mode, high purity, LG01 beam was generated with over 50% conversion efficiency
from a Gaussian mode using a complex-valued computer generated hologram (CGH) rendered
on a phase-only liquid-crystal spatial light modulator (SLM). A system-wide 35% conversion efficiency was achieved from the laser output to the vacuum chamber input.
Several micro-structured polymer optical fibres and silica hollow-core band-gap photonic crystal fibres with Kagome claddings were evaluated. A single defect, large hollow core
(50m diameter) Kagome cladding fibre was identified as a suitable solution for guiding cold 85Rb atoms.
This thesis explores hollow-core fibres as a platform for quantum optics experiments with laser-cooled atomic ensembles. The non-diffracting, tightly-confined guided modes of these fibers grant us a ~µm-wide one-dimensional space to study atom-light interactions. In order to describe on-going experiments, simulations are carried out to understand atomic motion into the hollow fibers. Following which, a preliminary case study of a quantum optics experiment to convert wavelengths of single photons with Cs atomic ensembles inside the hollow fiber is presented. Lastly, basic optical properties of photonic crystal membranes are briefly explored. These can form novel cavities when appended to hollow fibers.