The electron is predicted to have a small electric dipole moment (eEDM), although so far no one has been able to measure this experimentally. The size of the eEDM is strongly connected to how badly time-reversal (T) symmetry is broken by nature. The Standard Model of particle physics, which has a small amount of T violation, predicts an unmeasurably tiny eEDM: de < 10^(-38) e cm. However, it is suggested that there should be additional T-violating processes to account for the matter-antimatter asymmetry in the universe. These could lead to a detectable eEDM near to the current limit |de|< 8.7*10^(-29) e cm (90\% confidence). Ramsey spectroscopy on paramagnetic, polar molecules has proved a very effective method for measuring eEDMs. In this thesis I explain the progress that has been made towards using ytterbium fluoride (YbF) for a new, improved measurement of the eEDM. I discuss the current operation of the experiment, and the systematic effects connected with the experiment. The statistical uncertainty of the experiment in analysed, and shown to be dominated by photon counting statistics. Then, a list of improvements to the machine are described, and simulated using rate equations and the optical Bloch equations. Taken together, these improvements enhance the sensitivity of the experiment by a factor of eleven, thus, it can be used in the near future to make a world-leading measurement of the electron EDM.

The work presented in this thesis follows two main branches. The first aims to develop instrumentation for 3D-STED microscopy and to apply it to the study of bulk diamond, nanoparticles and biological samples. The second aims to evaluate the application of fluorescence imaging and spectroscopy techniques to the study of luminescent defects in diamond. Building on previous work in the Photonics Group at Imperial College London, spatial light modulator (SLM) technology was incorporated into a STED system in a novel configuration to provide a robust and convenient solution for 3D-STED microscopy. This system was applied to the first reported super-resolution imaging of the interaction between two cells in their natural state. The system was further applied to STED imaging of nitrogen vacancy centres in bulk diamond and to a proof of principle experiment for novel plasmon-assisted labels for STED microscopy. The effects of wavefront aberration on STED microscopy were investigated and a predictive correction philosophy was developed based on spherical aberration induced by a refractive index mismatch. The flexibility offered by the SLM technology was taken advantage of to demonstrate recovery of STED imaging quality in glycerol and bulk diamond by active correction of spherical aberration experienced by the depletion point spread function. Confocal intensity imaging, confocal fluorescence lifetime imaging (FLIM) and multispectral fluorescence lifetime measurement were applied to the imaging of fluorescent defects in bulk diamond. It was demonstrated that FLIM can provide information that is complimentary to intensity imaging in diamond and that it is possible to spectrally distinguish defects in diamond while simultaneously measuring their lifetime using multispectral lifetime measurement methods. This thesis also presents the ongoing development of a system for STED of live samples that express green fluorescent protein (GFP).

We have precisely characterised our Universe with the elegant LCDM model. However, this model predicts that around 70% of the Universe's content is dominated by a 'dark energy' that opposes gravity, and about 30% of its content is in some form of non-baryonic 'dark' matter that interacts only via gravity. Even when we consider the less exotic contents of our Universe, such as stars and galaxies, we are again forced to acknowledge the huge gaps in our knowledge. Observations of quasar spectra inform us that our Universe is in a highly ionized state during its later stages. However, from the cosmic microwave background we know that it was neutral for much of its history. It is sensible to assume that high-energy radiation, produced in abundance once stars and galaxies formed, would have driven the process of reionizing the Universe. However, the exact nature of early generations of stars and galaxies, and this process of reionization, are poorly constrained. In this work, we describe efforts to constrain the epoch of reionization, concentrating on the potential of the high-redshift 21-cm line of the hydrogen atom. Observations of the 21-cm signal would provide 3D maps of neutral hydrogen, and could provide vital constraints on the nature of reionization. Observing the 21-cm signal is challenging due to very strong radio foregrounds, we therefore concentrate on efforts to constrain the 21-cm signal statistically. In particular, we characterise the sensitivity of one-point statistics (or moments) of the 21-cm signal. We study the sensitivity of 21-cm moments to a wide range of morphological properties that might be exhibited by ionized bubbles during reionization. We then investigate how 21-cm moments are impacted by the details of inhomogeneous recombinations, where ionized hydrogen captures electrons to become neutral again. We then consider the sensitivity of 21-cm moments to the properties of X-ray production. This work is essential, as without fully understanding a statistic and how it depends on the underlying physical processes, we cannot hope to gain meaningful constraints from its observation. This work also exhibits how information rich the 21-cm moments are, providing strong motivation to better understand them, and for more effort to be put into constraining them from observations.

High temperature plasmas are ubiquitous in high energy astrophysics and are becoming increasingly accessible in the laboratory. This thesis is concerned with two interactions that are important in these systems. The first is the Coulomb interaction, which influences phenomena in systems ranging from controlled fusion experiments to catastrophic astrophysical events. In many of these cases, the motion of the electrons is relativistic. To account for this we extend Spitzer's famous work on dynamical friction in a plasma to relativistic interactions, deriving the Fokker-Planck coefficients and test particle relaxation rates in the same analytical form as Trubnikov's classical results. Following this, we present a self-consistent transport theory for a relativistic, magnetised plasma, including simple polynomial fits to the transport coefficients for various values of atomic number. This is the relativistic generalisation of the work of Braginskii and, within the confines of linear transport theory, is valid for all temperatures and field strengths of interest. These results are subsequently verified using Monte Carlo simulations, and the effects of non-Gaussian multiple scattering on transport in a plasma are shown to be small. Beyond relativistic corrections, high temperature plasmas are fundamentally different to their classical counterparts due to the possibility of pair production. One of the primary mechanisms for this and the second interaction we consider is the Breit-Wheeler process: the formation of an electron-positron pair in the collision of two photons. Despite being the simplest way in which light can be converted into matter, this process has never been directly observed in the laboratory. Here, we present a new design of photon-photon collider, in which a laser wakefield-driven gamma-ray beam is fired into the high temperature radiation field of a laser-heated hohlraum. On matching experimental parameters to current facilities, Monte Carlo simulations suggest this is capable of producing over 10^5 Breit-Wheeler pairs per shot.

Laser wakefield accelerators (LWFAs) operate through a high intensity ultra short laser pulse exciting a relativis- tic density wave in a plasma. I carried out experiments constructing LWFAs using lasers of a wide range of powers. Thereby allowing me to examine the generation of electrons and x-rays under these different conditions. The compar- ison of these results with my own and existing analytical models and computational modelling is discussed. In fulfilment of this, I developed novel techniques to measure hard x-rays in the tens of KeV energy range. In measure- ment of the relativistic electrons I found it possible to de- velop techniques to not only accurately measure the energy but also discern the three momentum vectors of electrons measured on a multiscreen electron spectrometer. As LWFAs open up the ability to produce high energy elec- tron beams without the need of tens of meters of RF accel- eration cavities and the lasers used to drive them can also be made relatively compact perhaps one of the most excit- ing application of this is the production of hard x-rays for imaging. As the source size of a LWFA betatron source is typically of micron scale, I investigated using LWFA derived x-rays for phase contrast imaging.

This thesis is focused on the development of an efficient first-principles theoretical and numerical method based on the many-electron algebraic diagrammatic construction [ADC(n)] schemes, in order to describe the correlated ionisation dynamics in atomic and molecular systems interacting with perturbative and non-perturbative laser fields. The first line of research has focused on the calculation of total single-photon photoionisation cross-sections, applying the Stieltjes-Imaging theory to Lanczos pseudospectra of the ADC Hamiltonian in Gaussian basis. We have established the accuracy of this technique by comparing the ADCLanczos-Stieltjes ground-state cross-sections obtained using different levels of many-body theory to the experimental ones for a series of organic molecules. We have extended this method to excited states cross-sections showing that a theoretical modelling of photoionisation from excited states requires an intrinsically double excitation theory. However, above 80 eV photon energy all three methods lead to inaccurate results due to the limitations of the Gaussian basis to describe continuum wave-functions of ionised electrons. The second, main line of research, has therefore been dedicated to constructing and computationally optimising the first implementation of the single [ADC(1)] and double excitations [ADC(2)] schemes in the B-spline basis, which is able to accurately describe the strongly oscillating continuum orbitals. As first application of this new method, we have calculated the photoionisation cross-sections of noble gas atoms showing that the features that pose a challenge for the GTO calculations are reproduced in a very good agreement with the experiment. We also have developed a time-dependent version with which we have calculated the HHG spectra of Ar, reproducing the effect of the Cooper minimum, and CO2, quantitatively investigating the multi-channel effects on its dynamical minimum. Finally we have provided a numerical answer to the highly topical question of coherence and ionic wavepacket formation in short pulse photoionisation.

No description available.

The use of Monte Carlo event generators for the simulation of LHC collider experiments, has in recent years driven a demand for greater accuracy of predictions in such generators. This thesis will be concerned with the addition of certain perturbative corrections in the event generator SHERPA. In this vein a framework for the automatic calculation of the real correction terms is presented, based on the the subtraction mechanism of of Frixione, Kunszt and Signer. This resulting framework is implemented in the matrix element generator Amegic, which will then allow the calculation of the real components of an NLO QCD for any process; this can be supplemented with virtual corrections to provide a full NLO QCD prediction. This implementation is then rigorously tested and found to be consistent with known NLO results. This subtraction framework is then utilized to perform a series of tests on the relative efficiency of the FKS and Catani Seymour subtraction methods; these tests are conducted over multiple processes and the affect of the multiplicity of the state is investigated. In addition the contribution of photon induced processes to lepton and W boson production is discussed, taking into account contributions from the QED part of parton distribution functions and from equivalent photons in the Weizsaecker Williams approximation. Typically these processes contribute on the per cent level compared to standard quark and gluon-induced processes; however, when applying various cuts this picture may change and the photon induced processes may become significant.

We present calculations of long-range interactions in Rydberg atoms, with a focus on the dipole-dipole interactions of strontium Rydberg states. The growing use of Rydberg states in the field of cold atoms necessitates a more detailed understanding of the effects of dipole-dipole interactions, which are currently being investigated in a number of research groups worldwide. Calculations of long-range interactions in Rydberg states of caesium, cal- cium, rubidium, strontium and ytterbium are presented. By taking the one active electron approximation we develop consistent models of these long- range interactions, and construct a survey of the Rydberg state dipole-dipole interactions and quadrupole-quadrupole interactions. We compare the inter- actions between series and between atoms, highlighting the importance of certain series for applications suggested in previous works. In order to include two-electron effects in the description of dipole-dipole interactions in divalent atoms, we use multichannel quantum defect theory (MQDT) to develop models of the Rydberg series of strontium. We use an empirical reactance matrix formalism, where the reactance matrix is fitted to reproduce experimentally measured values of the bound state energy levels. Models are found for all series of strontium with L ≤ 3. We extend the MQDT formalism to the description of the natural radiative lifetimes of strontium, where the perturbers are found to have a large quenching effect on these lifetimes. By incorporating the MQDT description of the Rydberg states of strontium into the calculation of dipole-dipole interactions, we find a spin-forbidden two-atom resonance in the 3D2 states of strontium. We consider a one- dimensional lattice of strontium atoms, and find that the internal dynamics of the Rydberg atoms demonstrates spin transport for large lattice spacings and a separation of the spin and total angular momentum dynamics for small lattice spacings. Spin-angular momentum separation (analogous to spin-charge separation in condensed matter) in strontium Rydberg atoms may have uses in the investigation of one-dimensional Fermi gases and their description using Luttinger liquid theory.

No description available.