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Thesis archive

Dave Author: Dr Gethin Richards
Title: Quantum coherent effects in the light-harvesting complex Phycocyanin 645
Completed: July 2014
Abstract: The light-harvesting complex Phycocyanin- 645(PC-645) is investigated using two-colour four-wave mixing spectroscopy. With this technique signals due to coherent superpositions are isolated, allowing detailed study of their dynamics and interactions within the light-harvesting complex.
Link: Thesis (pdf) (21 MB)
Dave Author: Dr Sascha Hoinka
Title: Precision Bragg spectroscopy of the density and spin response of a strongly interacting Fermi gas
Completed: May 2014
Abstract: This thesis presents precision measurements on strongly interacting Fermi gases using two-photon Bragg spectroscopy at high momentum (4.2 times the Fermi momentum). The universal contact parameter, an important many-body quantity governing the short-range and short-time properties of these systems, was determined to high accuracy in the low temperature limit providing a new benchmark for competing strong-coupling theories. Also, the dynamic spin response function was measured and shown to display a universal high-frequency tail. This was achieved by implementing a new type of Bragg scattering which opens the way to full characterisation of the static structure factor of atomic Fermi gases at any momentum.
Link: Thesis (pdf) (5 MB)
Dave Author: Dr Bogdan Opanchuk
Title: Quasiprobability methods in quantum interferometry of ultracold matter
Completed: January 2014
Abstract: A method of simulating the full quantum field dynamics of multimode, multi-component Bose-Einstein condensates is developed. The truncated Wigner representation is used to obtain a probabilistic theory. The representation is extended to to use a functional calculus and can be applied to quantum fields in the arbitrary number of dimensions.
Link: Thesis (pdf) (2 MB)
Dave Author: Dr David McDonald
Title: Polarisation Resolved Ultrafast Spectroscopic Investigation of Photoinduced Structural Dynamics in DCM dye
Completed: November 2013
Abstract: This thesis reports on the results of steady-state, polarisation and time-resolved spectroscopic investigations of the excited-state configurational dynamics of the well-known donor-acceptor dye molecule DCM. The aim of this study was to investigate the structural configuration of the excited-state or DCM and add to the discussion about the proposed, but controversial, existence of a twisted intramolecular charge transfer state in this molecule.
Link: Thesis (pdf) (6 MB)
Smitha Author: Dr Smitha Jose
Title: Trapping of ultracold atoms in a magnetic lattice
Completed: November 2013
Abstract: This thesis reports the trapping and evaporative cooling of ultracold 87Rb F = 1 atoms in a permanent magnetic lattice of period 10 μm integrated on an atom chip and evidence for the onset of quantum degeneracy in the magnetic lattice. The first clear evidence of achievement of quantum degeneracy in a magnetic lattice is demonstrated.
Link: Thesis (pdf) (13 MB)
Valentin Author: Dr Valentin Ivannikov
Title: Analysis of a trapped atom clock with losses
Completed: August 2013
Abstract: We present a number of analytical means for the analysis of the evolution of an atom clock, emphasizing the role of many-body processes in the population and coherence loss.
Link: Thesis (pdf) (8 MB)
Lena Author: Dr Elena Sinchenko
Title: Fibre Optic Distributed Corrosion Sensor
Completed: August 2013
Abstract: This thesis presents research towards the creation of a distributed optical fibre sensor for detecting corrosion at arbitrary points of interest in a large structure. The developed sensor is able to perform an important task of non-destructive evaluation and early warning of the corrosion situation. The method of corrosion detection is based on the principle of sensing of fluorescence using light as a probe and an optical fibre as a carrier. Theoretical models were elaborated to investigate and improve the efficiency of the optical fibre detection system. The potential for using the developed detection system in practical sensing applications was successfully demonstrated in a stimulated corrosion test.
Link: Thesis (pdf) (2.8 MB)
Khuong Author: Dr Ba Khuong Dinh
Title: Phase-Matched High Order Harmonic Generation and Applications
Completed: August 2012
Abstract: This dissertation reports experimental work based on the HHG technique. We present two novel schemes which can be used to enhance the quality of the HHG source including the conversion efficiency, the coherence and the cut-off photon energy. In the first scheme, a combination of lens and axicon is used to create a Bessel Gaussian beam instead of only a Gaussian beam and the presence of a new geometrical phase mismatch term is demonstrated. In the second scheme, the phase matching is controlled by a means of an off-axis beam.
Link: Thesis (pdf) (21 MB)
Mikhail Author: Dr Mikhail Egorov
Title: Coherence and collective oscillations of a two-component Bose-Einstein condensate
Completed: March 2012
Abstract: The research described in this thesis investigates, both theoretically and experimentally, the coherence and dynamical evolution of a two-component Bose-Einstein condensate (BEC). The studies are performed on the |F = 1,mF = -1> and |F = 2,mF = +1> hyperfine ground states of a 87Rb BEC trapped on an atom chip.
Link: Thesis (pdf) (8 MB)
Author: Dr Chris Hall
Title: Ultrafast Dynamics in Semiconductor Quantum Wells
Completed: November 2011
Abstract: Ultrafast spectroscopy has been used to explore two different quantum well systems. The first part of this thesis examines recombination dynamics of charge carriers in the presence of the built-in electric field in c-axis grown ZnO/MgZnO quantum wells. It is also shown that quantum wells with graded barriers can be used to control the wavefunction overlap integral between the lowest energy electron and hole states. In the second part of this thesis two-dimensional Fourier transform spectroscopy has been used to explore coherent coupling between excitons highly localized to different quantum wells in a series of GaAs/AlGaAs asymmetric double quantum wells.
Link: Thesis (pdf) (21 MB)
Russell Author: Dr Sasani Jayawardhana
Title: Development of Optical Fibre Chemical Probes by Oblique Angle Deposition
Completed: September 2011
Abstract: An optical fibre chemical sensor based on the technique of surface-enhanced Raman scattering (SERS) has been developed. SERS relies on the close interaction between the target analyte and a nanostructured metal surface. This nanostructure was fabricated using the method of oblique angle deposition (OAD) under thermal evaporation. The deposition was carried out by holding the sample surface at an oblique angle to the metal vapour flux, which results in a columnar morphology of the thin film. The potential for using the OAD substrate as an environmental sensor was investigated in the context of detecting atrazine, which is a common herbicide and water contaminant.
Link: Thesis (pdf) (14 MB)
Author: Dr Eva Kuhnle
Title: Studies of Universality in Strongly Interacting 6Li Fermi Gases with Bragg Spectroscopy
Completed: June 2011
Abstract: The principal topic of this thesis is the use of Bragg spectroscopy as a tool to measure the universal contact in trapped Fermi gases. The contact parameter quantifies the short-range pair correlation function according to a universal law. Inelastic Bragg scattering of photons allows one to measure the static structure factor, the universal relation for which is experimentally verified for a range of transferred momenta, k/kF = 3.5 - 9.1, in agreement with the theoretical predictions. The contact in the zero-temperature limit at different interaction strengths as well as in the unitarity limit at different temperatures agrees well with the calculations.
Link: Thesis (pdf) (3.2 MB)
Author: Dr Anthony Greaves
Title: Phase contrast in x-ray imaging
Completed: April 2011
Abstract: In clinical practice, polychromatic x-ray sources require filtering to remove the lower energy rays that have insufficient energy to penetrate the body and provide useful diagnostic information. However, the introduction of filters in propagation-based imaging is known to cause phase contrast degradation, and this thesis examines both experimentally and theoretically, the various factors affecting phase contrast.
Link: Thesis (pdf) (15.9 MB)
Russell Author: Dr Russell Anderson
Title: Nonequilibrium dynamics and relative phase evolution of two-component Bose-Einstein condensates
Completed: August 2010
Abstract: This thesis presents new experimental results on the relative phase evolution of two-component Bose-Einstein condensates. We approach our study of this system from the dual perspective of binary superfluidity and trapped atom interferometry. We observe nonequilibrium dynamics of the condensate that are deeply connected to the physics of interpenetrating superfluids. These dynamics have consequences for interferometers whose two paths are different internal spin states of the condensate atoms.
Link: Thesis (pdf) (22 MB)
Holger Author: Dr Paul Dyke
Title: Quasi Two-Dimensional 6Li Fermi gas
Completed: June 2010
Abstract: Quasi-2D degenerate Fermi gases provide a rich physical environment to explore since many effects that are present do not exist in 3D. This thesis describes the first experiments carried out in a quasi-2D Fermi gas across the broad 6Li Feshbach resonance at 834 G. The main experimental results are the first indications of a confinement induced resonance in a 6Li Fermi gas through the measurement of the cloud width in the tightly confined direction after a fixed expansion time.
Link: Thesis (pdf) (2.3 MB)
Holger Author: Dr Holger Wolff
Title: Femtosecond Ablation and Characterisation of Microfabricated Atom Chips
Completed: November 2009
Abstract: This thesis is focused on the application of a new microfabrication technique, femtosecond laser ablation, for the atom chip construction and on the characterisation of the physical and magnetic properties of microwire structures. Femtosecond ablation was demonstrated to efficiently remove submicron thick layers of metal for structural shape changes in a one-step procedure.
Link: Thesis (pdf) (3.7 MB)
Gopi Author: Dr Sven Teichmann
Title: High Harmonic Generation for Coherent Diffractive Imaging
Completed: November 2009
Abstract: This dissertation presents experimental work on a high-harmonic generation source and coherent diffractive imaging. A novel and successful approach of employing harmonic emission that consists of multiple harmonic orders and its utilization for coherent diffractive imaging is presented, and associated results are discussed. This work may prove valuable particularly for time-resolved spectroscopy, sources of soft x-ray and extreme-ultraviolet radiation, and imaging based on harmonic emission.
Link: Thesis (pdf) (9.3 MB)
Gopi Author: Dr Gopi Veeravalli
Title: Bragg Spectroscopy of a Strongly Interacting Fermi Gas
Completed: August 2009
Abstract: The main objective of the research described in this thesis is to probe the manybody quantum effects in a strongly interacting Fermi gas using Bragg spectroscopy. An enriched source of Lithium-6 atoms is used to probe these properties. The broad Feshbach resonance of the two lowest hyperfine levels of 6Li at a magnetic field of 834G is exploited to precisely control the interactions between the atoms.
Link: Thesis (pdf)
Jurgen Author: Dr Jurgen Fuchs
Title: Molecular Bose-Einstein Condensates and p-wave Feshbach Molecules of 6Li2
Completed: January 2009
Abstract: This thesis describes the production of molecular Bose-Einstein condensates (BEC) of 6Li2 dimers and binding energy measurements of p-wave Feshbach molecules formed in combinations of the |F = 1/2,mF = +1/2> (|1>) and |F = 1/2,mF = -1/2>(|2>) states. The binding energies scale linearly with magnetic field detuning for all three resonances. The relative molecular magnetic moments are found to be 113±7 μK/G, 111±6 μK/G and 118±8 μK/G for the |1> - |1>, |1> - |2> and 2> - |2> resonances, respectively, in good agreement with theoretical predictions.
Link: Thesis (pdf)
Mandip Author: Dr Mandip Singh
Title: A Magnetic Lattice and Macroscopic Entanglement of a BEC on an Atom Chip
Completed: December 2008
Abstract: The research work presented in this thesis is classified in two major categories. The first part is focused on the development and construction of a permanent magnetic lattice on an atom chip and the study of trapped atoms in the permanent magnetic lattice potential. In the second part, a new experiment is proposed to create a macroscopic entanglement between the flux state of a superconducting loop and a Bose-Einstein condensate (BEC) on a superconducting atom chip.
Link: Thesis (pdf)
Dan Author: Dr Daniel White
Title: Nanostructured Optical Fibre for use as Miniature Surface-enhanced Raman Scattering Sensors
Completed: October 2008
Abstract: This thesis invesitigates the use of an optical fibre based SERS system. The fibres are based on highly modified medical imaging fibres consisting of a fused bundle of single-mode fibres ("pixels") drawn in such a way that each fibre maintains its position along the length of the bundle. A selective chemical etchant is used to erode the cores of these fibres leaving an array of wells. By drawing the fibre until the spacing between the cores is of the order of hundreds of nanometres, the etched structures are suitable for SERS after coating with a thin layer of metal. As a practical demonstration of the use of the SERS fibres, experiments on the detection of glucose, CEES (a simulant for the nerve agent HD mustard) and chlorsulphuron (a commonly used herbicide), were conducted.
Link: Thesis (pdf)
Tra My Author: Dr Tra My Do
Title: Femtosecond Nonlinear Coherent Spectroscopy of Carotenoids
Completed: September 2008
Abstract: In this thesis femtosecond spectrally resolved one- and two-colour four-wave mixing coherent spectroscopy is used to study the population dynamics and coherence dynamics in two carotenoids, lycopene (with eleven conjugated carbon bonds (C=C), n = 11) and spheroidene (n = 10), in n-hexane solution. This information could play an important role in elucidating the light harvesting function of lycopene and spheroidene in the process of photosynthesis.
Link: Thesis (pdf)
Saeed Author: Dr Saeed Ghanbari
Title: Superfluid to Mott insulator quantum phase transition in permanent magnetic lattices
Completed: March 2008
Abstract: In this thesis we study quantum degenerate Bose gases at finite temperatures in optical and magnetic lattices and in particular the superfluid to Mott insulator quantum phase transition. We investigate ultracold atoms with the gauge P representation and a truncated number-state basis. We consider a grand canonical ensemble of Bose gases and use the Bose-Hubbard model which can describe the dynamics of ultracold atoms in periodic potentials such as optical and magnetic lattices. In our calculations, we consider open boundary conditions.
Link: Thesis (pdf)
Heath Author: Dr Heath Kitson
Title: Experiments on Ultracold Rb: Rydberg atoms and Rb2 molecules
Completed: January 2008
Abstract: This thesis presents experiments done in both 85Rb and 87Rb magneto optical traps. Fluorescence techniques are employed for the initial characterisation of atom number, density, temperature, loading and collisional rates in the trap. Spectroscopy of atomic energy levels over most of the optical spectrum is presented for 85Rb, using a two-photon ionisation technique. The atomic nd states where n=6-42 are resolved over an energy range of 15,800 - 20,800 cm-1. An additional broad series of peaks following the nd series is observed but their origin could not be identified.
Link: Thesis (pdf)
Falk Author: Dr Falk Scharnberg
Title: Bose-Einstein Condensation in Micro-Potentials for Atom Interferometry
Completed: October 2007
Abstract: Recent developments in atom optics have led to new proposals for interferometers, where the splitting takes place spatially. Magnetic and optical traps are both suited for this kind of interferometer if a well defined and highly controllable trap is realised. In this thesis results from two experiments that in principle allow the creation of such traps are presented.
Link: Thesis (pdf)
Craig Author: Dr Craig Lincoln
Title: Multidimensional nonlinear femtosecond spectroscopy of biological molecules
Completed: July 2007
Abstract: The new technique of two-colour spectrally resolved photon echo spectroscopy, is applied to the biological system carbonmonoxy myoglobin (MbCO). This study provides supporting evidence for the mechanics of the initial steps involved in the light-induced photodissociation of MbCO to form deoxy-myoglobin. A number of photophysical phenomena associated with the reaction are investigated.
Link: Thesis (pdf)
Shannon Author: Dr Shannon Whitlock
Title: Bose-Einstein condensates on a magnetic film atom chip
Completed: April 2007
Abstract: Atom chips are devices used to magnetically trap and manipulate ultracold and Bose-Einstein condensates near a surface. In particular, permanent magnetic atom chips can allow very tight confinement and intricate magnetic field designs circumventing technical current noise. Research described in this thesis is focussed on the development of a magnetic film atom chip, the production of Bose-Einstein condensates near the film surface, the characterisation of the associated magnetic potentials using rf spectroscopy of ultracold atoms and the realisation of a precision sensor based on splitting Bose-Einstein condensates in a double-well potential.
Link: Thesis (pdf)
Wen Author: Dr Xiaoming Wen
Title: Ultrafast spectroscopy of semiconductor nanostrucrures
Completed: April 2007
Abstract: The key to designing and utilising semiconductor quantum structures is a physical understanding of the detailed excitation, transport and energy relaxation processes. This thesis reports investigations into the electronic and optical properties of various semiconductor quantum systems using a variety of ultrafast techniques, including up-conversion photoluminescence, pump-probe, photon echoes and four-wave mixing.
Link: Thesis (pdf)