Diode-pumped alexandrite laser development and vortex mode generation

This thesis is focussed on two aspects of solid-state laser development: optimising and understanding diode-pumped Alexandrite laser performance, and a new laser cavity design for vortex mode generation. Due to its broad wavelength tunability (700nm to 858nm) and excellent physical properties, Alexandrite has a wide range of potential applications from remote sensing to quantum optics. Recent advances in red laser diode-pumping has enabled high power and efficient laser operation. In this work a continuous-wave analytical model of end-pumped Alexandrite lasers was developed and applied to experimental systems. This helped to achieve a record diode-pumped slope efficiency of 54% with 1.2W of output power. A record shortest wavelength (714nm) and broadest tuning range (104nm) was obtained through optimising the crystal temperature between 8 °C and 105 °C. Investigation and new measurements of the properties of Alexandrite gave rules applicable in general to optimising these lasers, along with assessing the fundamental limits to Alexandrite laser efficiency. Optical vortex laser beams have attracted considerable attention from their wide range of applications that cover many areas of science, from optical communications to laser machining to microscopic laser manipulation. Directly generating them from a laser has advantages due to the pure and high power modes that can be generated. In this work an anti-resonant ring was proposed and used to couple two lasers through a shared gain medium. Using one cavity to control the output of the other, first order vortex Laguerre-Gaussian modes of power 9.0W from 24W of input power with high quality (M² = 2.1) were obtained, which had controllable and pure handedness. A second order vortex mode with 4.3W of power was also created. This vortex generation geometry could be applied to any solid-state laser gain medium, which would enable vortex generation across the electromagnetic spectrum.Open Acces

Temperature effects on tunable CW Alexandrite lasers under diode end-pumping

Diode pumped Alexandrite is a promising route to high power, efficient and inexpensive lasers with a broad (701 nm to 858 nm) gain bandwidth; however, there are challenges with its complex laser dynamics. We present an analytical model applied to experimental red diode end-pumped Alexandrite lasers, which enabled a record 54 % slope efficiency with an output power of 1.2 W. A record lowest lasing wavelength (714 nm) and record tuning range (104 nm) was obtained by optimising the crystal temperature between 8 °C and 105 °C in the vibronic mode. The properties of Alexandrite and the analytical model were examined to understand and give general rules in optimising Alexandrite lasers, along with their fundamental efficiency limits. It was found that the lowest threshold laser wavelength was not necessarily the most efficient, and that higher and lower temperatures were optimal for longer and shorter laser wavelengths, respectively. The pump excited to ground state absorption ratio was measured to decrease from 0.8 to 0.7 by changing the crystal temperature from 10 °C to 90 °C

Cold War Fictions

This chapter offers a detailed reading of McEwan’s 2012 novel Sweet Tooth as a highly self-conscious and allusive literary spy thriller of the Cold War era, one which invites a renewed attention to the Cold War themes, ideas and literary strategies which have been important in his work since the late 1970s in which the novel is set. These flourished especially in the two novels written around the fall of the Berlin Wall, The Innocent and Black Dogs which also receive extended treatment here. In McEwan’s reworking of the Cold War spy thriller as postmodern literary fiction we find, it is argued, a recurrent fascination with misunderstandings and readjustments in emotional and political relations between the sexes as an analogy for Cold War politics and vice versa. Added to this McEwan increasingly packs his fictions with informed literary debate that constitute a profound exploration of literary genres and of the complex relationship between author and reader

Abstracts from the NIHR INVOLVE Conference 2017

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Measurement and interpretation of same-sign W boson pair production in association with two jets in pp collisions at s = 13 TeV with the ATLAS detector

This paper presents the measurement of fducial and diferential cross sections for both the inclusive and electroweak production of a same-sign W-boson pair in association with two jets (W±W±jj) using 139 fb−1 of proton-proton collision data recorded at a centre-of-mass energy of √s = 13 TeV by the ATLAS detector at the Large Hadron Collider. The analysis is performed by selecting two same-charge leptons, electron or muon, and at least two jets with large invariant mass and a large rapidity diference. The measured fducial cross sections for electroweak and inclusive W±W±jj production are 2.92 ± 0.22 (stat.) ± 0.19 (syst.)fb and 3.38±0.22 (stat.)±0.19 (syst.)fb, respectively, in agreement with Standard Model predictions. The measurements are used to constrain anomalous quartic gauge couplings by extracting 95% confdence level intervals on dimension-8 operators. A search for doubly charged Higgs bosons H±± that are produced in vector-boson fusion processes and decay into a same-sign W boson pair is performed. The largest deviation from the Standard Model occurs for an H±± mass near 450 GeV, with a global signifcance of 2.5 standard deviations

Studies of new Higgs boson interactions through nonresonant HH production in the b¯bγγ fnal state in pp collisions at √s = 13 TeV with the ATLAS detector

A search for nonresonant Higgs boson pair production in the b ¯bγγ fnal state is performed using 140 fb−1 of proton-proton collisions at a centre-of-mass energy of 13 TeV recorded by the ATLAS detector at the CERN Large Hadron Collider. This analysis supersedes and expands upon the previous nonresonant ATLAS results in this fnal state based on the same data sample. The analysis strategy is optimised to probe anomalous values not only of the Higgs (H) boson self-coupling modifer κλ but also of the quartic HHV V (V = W, Z) coupling modifer κ2V . No signifcant excess above the expected background from Standard Model processes is observed. An observed upper limit µHH < 4.0 is set at 95% confdence level on the Higgs boson pair production cross-section normalised to its Standard Model prediction. The 95% confdence intervals for the coupling modifers are −1.4 < κλ < 6.9 and −0.5 < κ2V < 2.7, assuming all other Higgs boson couplings except the one under study are fxed to the Standard Model predictions. The results are interpreted in the Standard Model efective feld theory and Higgs efective feld theory frameworks in terms of constraints on the couplings of anomalous Higgs boson (self-)interactions

Model-independent search for the presence of new physics in events including H → γγ with s \sqrt{s} = 13 TeV pp data recorded by the ATLAS detector at the LHC

Abstract A model-independent search for new physics leading to final states containing a Higgs boson, with a mass of 125.09 GeV, decaying to a pair of photons is performed with 139 fb−1 of s $$\sqrt{s}$$ = 13 TeV pp collision data recorded by the ATLAS detector at the Large Hadron Collider at CERN. This search examines 22 final states categorized by the objects that are produced in association with the Higgs boson. These objects include isolated electrons or muons, hadronically decaying τ-leptons, additional photons, missing transverse momentum, and hadronic jets, as well as jets that are tagged as containing a b-hadron. No significant excesses above Standard Model expectations are observed and limits on the production cross section at 95% confidence level are set. Detector efficiencies are reported for all 22 signal regions, which can be used to convert detector-level cross-section limits reported in this paper to particle-level cross-section constraints