[en] This thesis presents an experimental investigation into the brightness of high harmonic radiation produced during the interaction of high power lasers with both gaseous and solid targets. High harmonics of optical and UV (ultraviolet) lasers represent one of the most favourable ways of generating short pulse coherent radiation in the extreme ultraviolet (XUV) region of the electromagnetic spectrum. For harmonics produced via gas target interactions the yield is optimised for wavelengths between 35 and 11 nm generated from a many times diffraction limited 248 nm UV laser. The results show over an order of magnitude improvement on previous measurements even for these non-optimal laser conditions. Good agreement to the data is found with code simulations which show possibilities for further increases in brightness at these and shorter wavelengths from a better quality laser driver. From a 1.053 μm laser-solid target interaction experiment the first ever measurement of the harmonic brightness is presented. Using simple scaling laws the expected brightness at higher laser intensities is inferred, and possible methods of improving the source parameters with improved laser conditions are discussed. A comparison is then made of the relative brightness of the harmonics produced via the gaseous and solid target interactions and with current X-ray lasers. Finally an experimental feasibility study is presented utilising a 248 nm UV driving laser for solid target harmonic generation. These results show good agreement with code simulations including appropriate plasma conditions. (author)

[en] Several groups have developed miniaturized sector mass spectrometers with the goal of remote sensing in confined spaces or portability. However, these achievements have been overshadowed by more successful development of man-portable quadrupole and ion trap mass spectrometers. Despite these accomplishments the development of a reduced-scale sector mass spectrometer remains attractive as a potentially low-cost, robust instrument requiring very simple electronics and low power. Previous studies on miniaturizing sector instruments include the use of a Mattauch-Herzog design for a portable mass spectrograph weighing less than 10 kg. Other work has included the use of a Nier-Johnson design in spacecraft-mountable gas chromatography mass spectrometers for the Viking spacecraft as well as miniature sector-based MS/MS instrument. Although theory for designing an optimized system with high resolution and mass accuracy is well understood, such specifications have not yet been achieved in a miniaturized instrument. To proceed further toward the development of a miniaturized sector mass spectrometer, experiments were conducted to understand and optimize a practical, yet nonideal instrument configuration. The sector mass spectrometer studied in this work is similar to the ones developed for the Viking project, but was further modified to be low cost, simple and robust. Characteristics of this instrument that highlight its simplicity include the use of a modified Varian leak detector ion source, source ion optics that use one extraction voltage, and an unshunted fixed nonhomogeneous magnetic sector. The effects of these design simplifications on ion trajectory were studied by manipulating the ion beam along with the magnetic sector position. This latter feature served as an aid to study ion focusing amidst fringing fields as well as nonhomogeneous forces and permitted empirical realignment of the instrument

[en] The emission spectrum from a plasma is often used to extract information on the hydrodynamic, radiative and atomic processes that take place. As these processes are coupled, detailed interpretation of spectroscopic data is often complex and uncertain. We present an experiment and modelling study of a 'simple' hydrogen and helium-like plasma. The target and laser geometry were designed to minimise spatial gradients transverse to the plasma flow. The plasma was spatially and temporally diagnosed using Thomson scattering, X-ray imaging and spectroscopic measurements. The combination of the optical and X-ray results constrains the numerical modelling to provide a more reliable plasma diagnostic. This is essential for the interpretation of high-resolution measurements and of more complex, non 1-dimensional plasmas. Optical parameters of the plasma parameters inferred independently of the X-ray measurements, were used to test the accuracy of hydrodynamic simulations made using the EHYBRID code. The densities from EHYBRID were compared to those from planar MED103 simulations and found to be in reasonable agreement. The EHYBRID electron temperatures were found to be similar to values inferred from Thomson scattering measurements. These results suggest that EHYBRID can reasonably simulate the 1-dimensional plasma

[en] Measurement of magnetic fields generated by a high-energy, high-intensity laser-driven millimeter-scale Helmholtz coil target is reported. The magnetic field is derived from a reverse current that passes through two coils of 1.25-mm radius. A peak field of 7 T with a time decay of 17 ns is inferred from a series of induction coil measurements when the hot-electron temperature driving the reverse current is approximately ∼15 keV. A simple model of the laser-driven Helmholtz coil target suggests how the target should be optimized to produce high-peak fields and indicates that peak magnetic fields above 100 T are accessible. This could lead to exciting experiments in laser-plasma physics, in particular, experiments related to laboratory astrophysics

[en] We report an analysis of absorption and fluorescence spectroscopy of the interaction of Al XIII Ly-α radiation with Fe XXIV in laser-produced plasmas. These results were obtained in the context of exploring a Al-Fe photopumped X-ray laser scheme. Aluminium/iron targets were used in different geometries in order to observe in detail the transition mechanisms of the Al/Fe photopumping scheme. The absorption of the Al XIII Ly-α emission by the Fe XXIV plasma was observed after traversing different lengths of an Fe plasma. A simple radiation transfer model is being developed as a post-processor to the 1-D hydro-code MED103 in order to simulate these results. We also report some experimental evidence that may indicate that enhanced fluorescence of Fe XXIV 5d-2p transition could have occurred due to photopumping by the Al radiation despite any direct evidence of photopumped XUV lasing

[en] A number of detection methods for irradiated foods are in advanced state of development. No single method is likely to be universally applicable but a battery of tests such as thermoluminescence, electron spin resonance and analysis of lipid radiolytic products may soon be available for most foods and technical uses of irradiation. Most of these proposed tests require relatively sophisticated equipment or technical skills and are often time consuming and costly. There would be value in relatively simple tests which could be used as a rapid screening system or confirmatory method. The literature on the use of radiolytic gases as a detection method is limited and this paper extends the above studies. In particular, it extends the work to frozen shellfish, for which irradiation has been used as a commercial decontaminant technique for many years, and considers the effect of storage temperature. Work on poultry is also reported as a cross-reference to earlier work and because irradiated poultry has recently been released into the US retail trade. (author)

[en] Results from an experimental study of the collisionless interaction of two laser-produced plasmas in a magnetic field with applications to supernova remnant shock physics are presented. The dynamics of the two plasmas and their interaction are studied with and without magnetic field through spatially and temporally resolved measurements of the electron density. Experimental results show that counter-propagating collisionless plasmas interpenetrate when no magnetic field is present. In contrast, results obtained with the addition of a 7.5 T magnetic field perpendicular to plasma flow show density features in the interaction area that only occur when the field is present. The reason for this remains uncertain. It is suggested that this results from an increase in the effective collisionality as the magnetic field reduces the ion and electron gyroradius below the size of the experiment

[en] Laboratory astro-plasma physics experiments are being designed to advance both our astrophysics and plasma physics knowledge. With current laser technology, target design and diagnostics, it is now possible to reproduce and measure the conditions of temperature and pressure usually met in extreme stellar environments. Coupled with scaled plasma physics it is possible to simulate certain aspects of astrophysical phenomena in the laser laboratory. The focus is on experiments designed to address key aspects of the plasma physics occurring in supernova remnants. In this approach ideal magneto-hydrodynamics is applied to the supernova remnant and then scaled. Matching dimensionless parameters in a laboratory experiment enables the simulation of complex astro-plasma systems offering the advantage of repeated, detailed measurements and the flexibility to alter the input conditions. Work at York has centered on developing a collisionless plasma experiment. The experiment involves a magnetic field, and two laser-exploded plasmas to make possible a laboratory study of the interaction between a supernova remnant and the interstellar medium. These experiments and the analysis are discussed

[en] A 3.4 ps duration, high-repetition rate laser is used to create an aluminium ablation plasma at intensities between 10¹⁵ W/cm² and 10¹⁷ W/cm². K-shell emission is observed from the target surface and several 100 μm in to the plume. High resolution, spatial resolved measurements of the Heβ (1s3p - 1s²), Heγ (1s4p - 1s²), Heδ (1s6p - 1s²) transitions are obtained using a highly dispersive toroidal crystal spectrometer coupled to a large area charged-coupled device. This data shows unusual intensity modulations on Heβ transitions. These oscillations are observed to 50 μm above the target and are found to be reproducible, and the intensity of the modulations is laser irradiance dependent. (authors)

[en] The characteristics of 22-40 keV Kα x-ray sources are measured. These high-energy sources are produced by 100 TW and petawatt high-intensity lasers and will be used to develop and implement workable radiography solutions to probe high-Z and dense materials for the high-energy density experiments. The measurements show that the Kα source size from a simple foil target is larger than 60 μm, too large for most radiography applications. The total Kα yield is independent of target thicknesses, verifying that refluxing plays a major role in photon generation. Smaller radiating volumes emit brighter Kα radiation. One-dimensional radiography experiments using small-edge-on foils resolved 10 μm features with high contrast. Experiments were performed to test a variety of small volume two-dimensional point sources such as cones, wires, and embedded wires, measured photon yields, and compared the measurements with predictions from hybrid-particle-in-cell simulations. In addition to high-energy, high-resolution backlighters, future experiments will also need imaging detectors and diagnostic tools that are workable in the high-energy range. An initial look at some of these detector issues is also presented