The TARANIS laser : A multi-terawatt system for laser plasma physics

The Terawatt Apparatus for Relativistic And Non-linear Interdisciplinary Science (TARANIS), installed in the Centre for Plasma Physics at the Queen's University Belfast, supports a wide ranging science program, including laser-driven particle acceleration, X-ray lasers and high energy density physics experiments. We present (1) an overview of the laser facility, (2) results of preliminary investigations on proton acceleration, laser action at 13.9 nm and Kα sources and (3) speculation on future experiments using these extreme sources.

Laser-driven x-ray and neutron source development for industrial applications of plasma accelerators

Pulsed beams of energetic x-rays and neutrons from intense laser interactions with solid foils are promising for applications where bright, small emission area sources, capable of multi-modal delivery are ideal. Possible end users of laser-driven multi-modal sources are those requiring advanced non-destructive inspection techniques in industry sectors of high value commerce such as aerospace, nuclear and advanced manufacturing. We report on experimental work that demonstrates multi-modal operation of high power laser-solid interactions for neutron and x-ray beam generation. Measurements and Monte Carlo radiation transport simulations show that neutron yield is increased by a factor ∼2 when a 1 mm copper foil is placed behind a 2 mm lithium foil, compared to using a 2 cm block of lithium only. We explore x-ray generation with a 10 picosecond drive pulse in order to tailor the spectral content for radiography with medium density alloy metals. The impact of using >1 ps pulse duration on laser-accelerated electron beam generation and transport is discussed alongside the optimisation of subsequent bremsstrahlung emission in thin, high atomic number target foils. X-ray spectra are deconvolved from spectrometer measurements and simulation data generated using the GEANT4 Monte Carlo code. We also demonstrate the unique capability of laser-driven x-rays in being able to deliver single pulse high spatial resolution projection imaging of thick metallic objects. Active detector radiographic imaging of industrially relevant sample objects with a 10 ps drive pulse is presented for the first time, demonstrating that features of 200 μm size are resolved when projected at high magnification.

Investigations of ultrafast charge dynamics in laser-irradiated targets by a self probing technique employing laser driven protons

The divergent and broadband proton beams produced by the target normal sheath acceleration mechanism provide the unique opportunity to probe, in a point-projection imaging scheme, the dynamics of the transient electric and magnetic fields produced during laser-plasma interactions. Commonly such experimental setup entails two intense laser beams, where the interaction produced by one beam is probed with the protons produced by the second. We present here experimental studies of the ultra-fast charge dynamics along a wire connected to laser irradiated target carried out by employing a ‘self’ proton probing arrangement – i.e. by connecting the wire to the target generating the probe protons. The experimental data shows that an electromagnetic pulse carrying a significant amount of charge is launched along the wire, which travels as a unified pulse of 10s of ps duration with a velocity close to speed of light. The experimental capabilities and the analysis procedure of this specific type of proton probing technique are discussed.

Mechanical behaviour of AISiC nano composites produced by Ball Milling and Spark Plasma Sintering

Neste trabalho foram produzidos nanocompósitos de AlSiC misturando alumínio puro com nano partículas de SiC com diâmetro de 45 – 55 nm, usando, de forma sequencial, a técnica da metalurgia do pó e a compactação por “ Spark Plasma Sintering”. O compósito obtido apresentava grãos com 100 nm de diâmetro, encontrandose as partículas de SiC localizadas, principalmente, nas fronteiras de grão. O nanocompósito sob a forma de provetes cilíndricos foi submetido a testes de compressão uniaxial e a testes de nanoindentação para analisar a influência das nanopartículas de SiC, da fração volúmica de ácido esteárico e do tempo de moagem, nas propriedades mecânicas do material. Para efeitos de comparação, utilizouse o comportamento mecânico do Al puro processado em condições similares e da liga de alumínio AA1050O. A tensão limite de elasticidade do nanocompósito com 1% Vol./Vol. de SiC é dez vezes superior à do AA1050. O refinamento de grão à escala nano constitui o principal mecanismo de aumento de resistência mecânica. Na realidade, o Al nanocristalino sem reforço de partículas de SiC, apresenta uma tensão limite de elasticidade sete vezes superior à da liga AA1050O. A adição de 0,5 % Vol./Vol. e de 1 % Vol./Vol. de SiC conduzem, respetivamente, ao aumento da tensão limite de elasticidade em 47 % e 50%. O aumento do tempo de moagem e a adição de ácido esteárico ao pó durante a moagem conduzem apenas a um pequeno aumento da tensão de escoamento. A dureza do material medida através de testes de nanoindentação confirmaram os dados anteriores. A estabilidade das microestruturas do alumínio puro e do nanocompósito AlSiC, foi testada através de recozimento de restauração realizado às temperaturas de 150 °C e 250 °C durante 2 horas. Aparentemente, o tratamento térmico não influenciou as propriedades mecânicas dos materiais, excepto do nanocompósito com 1 % Vol./Vol. de SiC restaurado à temperatura de 250 °C, para o qual se observou uma redução da tensão limite de elasticidade na ordem dos 13 %. No alumínio nanocristalino, a tensão de escoamento é controlada pelo efeito de HallPetch. As partículas de SiC, são segregadas pelas fronteiras do grão e não contribuem para o aumento de resistência mecânica segundo o mecanismo de Orowan. Alternativamente, as nanopartículas de SiC constituem um reforço das fronteiras do grão, impedindo o seu escorregamento e estabilizando a nanoestrutura. Deste modo, as propriedades mecânicas do alumínio nanocristalino e do nanocompósito de AlSiC poderão estar relacionadas com a facilidade ou dificuldade do escorregamento das fronteiras de grão, embora não seja apresentada prova explícita deste mecanismo à temperatura ambiente.

Effect of ambient gas on the expansion dynamics of plasma plume formed by laser blow off of thin film

A study has been carried out to understand the influence of ambient gases on the dynamics of laser-blow-off plumes of multi-layered LiF–C thin film. Plume images at various time intervals ranging from 100 to 3000 ns have been recorded using an intensified CCD camera. Enhancement in the plume intensity and change in size and shape occurs on introducing ambient gases and these changes are highly dependent on the nature and composition of the ambient gas used. Velocity of the plume was found to be higher in helium ambient whereas intensity enhancement is greater in argon environment. The plume shapes have maximum size at 10−2 and 10−1 Torr of Ar and He pressures, respectively. As the background pressure increases further (>10−2 Torr: depending on the nature of gas), the plume gets compressed/focused in the lateral direction. Internal structure formation and turbulences are observed at higher pressures (>10−1 Torr) in both ambient gases.

Nd:Glass laser-induced damage to thin films, two-photon excited fluorescence and plasma studies

Laser-induced damage is the principal limiting constraint in the design and operation of high-power laser systems used in fusion and other high-energy laser applications. Therefore, an understanding of the mechanisms which cause the radiation damage to the components employed in building a laser and a knowledge of the damage threshold of these materials are of great importance in designing a laser system and to operate it without appreciable degradation in performance. This thesis, even though covers three distinct problems for investigations using a dye Q-switched multimode Nd:glass laser operating at 1062 nm and emitting 25 ns (FWHM) pulses, lays its main thrust on damage threshold studies on thin films. Using the same glass laser two-photon excited fluorescence in rhodamine 6G and generation and characterisation of a carbon plasma have also been carried out. The thesis is presented in seven chapters.

Nd:Glass Laser-Induced Damage To Thin Films, Two-Photon Excited Fluorescence And Plasma Studies

Laser-induced damage is the principal limiting constraint in the design and operation of high-power laser systems used in fusion and other high-energy laser applications. Therefore, an understanding of the mechanisms which cause the radiation damage to the components employed in building a laser and a knowledge of the damage threshold of these materials are of great importance in designing a laser system and to operate it without appreciable degradation in performance. This thesis, even though covers three distinct problems for investigations using a dye Q-switched multimode Nd:glass laser operating at 1062 nm and emitting 25 ns (FWHM) pulses, lays its main thrust on damage threshold studies on thin films. Using the same glass laser two-photon excited fluorescence in rhodamine 6G and generation and characterisation of a carbon plasma have also been carried out.

Nanostructured europium oxide thin films deposited by pulsed laser ablation of a metallic target in a He buffer atmosphere

Nanostrucured europium oxide and hydroxide films were obtained by pulsed Nd:YAG (532 nm) laser ablation of a europium metallic target, in the presence of a 1 mbar helium buffer atmosphere. Both the produced film and the ambient plasma were characterized. The plasma was monitored by an electrostatic probe, for plume expansion in vacuum or in the presence of the buffer atmosphere. The time evolution of the ion saturation current was obtained for several probe to substrate distances. The results show the splitting of the plume into two velocity groups, being the lower velocity profile associated with metal cluster formation within the plume. The films were obtained in the presence of helium atmosphere, for several target-to-substrate distances. They were analyzed by Rutherford backscattering spectrometry, x-ray diffraction, and atomic force microscopy, for as-deposited and 600 degrees C treated-in-air samples. The results show that the as-deposited samples are amorphous and have chemical composition compatible with europium hydroxide. The thermally treated samples show x-ray diffraction peaks of Eu(2)O(3), with chemical composition showing excess oxygen. Film nanostructuring was shown to be strongly correlated with cluster formation, as shown by velocity splitting in probe current versus time plots. (C) 2010 American Vacuum Society. [DOI: 10.1116/1.3457784]

Redução aluminotérmica do óxido de tântalo usando uma tocha de plasma como ignitor

In this work was used a plasma torch of non transferred arc with argon as work gas, using a power supply with maximum DC current of 250 A and voltage of 30 V to activate the plasma and keep it switched on. The flame temperature was characterized by optical emission spectroscopy, through Boltzmann-plot-method. The torch has been used like igniter in the aluminothermic reduction of the mixture tantalum oxide and aluminum, seeking to obtain metallic tantalum. In heating of the reagents only one particle will be considered to study interactions between plasma-particle, seeking to determinate its fusion and residence time. The early powders were characterized by laser granulometry, scanning electron microscopy (SEM) and X-ray diffraction analysis. The final product of this reaction was characterized by SEM and X-ray diffraction. Crystallite size was calculated by the Scherrer equation and microdeformation was determined using Willamsom-Hall graph. With Rietveld method was possible to quantify the percentile in weight of the products obtained in the aluminothermic reaction. Semi-quantitative chemical analysis (EDS) confirmed the presence of metallic tantalum and Al2O3 as products of the reduction. As was waited the particle size of the metallic tantalum produced, presents values in nanometric scale due the short cooling time of those particles during the process

Polyurethane coating with thin polymer films produced by plasma polymerization of diglyme

Aqueous-based polyurethane dispersions have been widely utilized as lubricants in textile, shoes, automotive, biomaterial and many other industries because they are less aggressive to surrounding environment. In this work thin films with different thickness were deposited on biocompatible polyurethane by plasma polymerization process using diethylene glycol dimethyl ether (Diglyme) as monomer. Molecular structure of the films was analyzed by Fourier Transform Infrared spectroscopy. The spectra exhibited absorption bands of O-H (3500-3200cm(-1)), C-H (3000-2900cm(-1)), C=O (1730-1650cm(-1)), C-O and C-O-C bonds at 1200-1600cm(-1). The samples wettability was evaluated by measurements of contact angle using different liquids such as water, glycerol, poly-ethane and CMC. The polyurethane surface showed hydrophilic behavior after diglyme plasma-deposition with contact angle dropping from 85(0) to 22(0). Scanning Electron Microscopy revealed that diglyme films covered uniformly the polyurethane surfaces ensuring to it a biocompatible characteristic.

RELATIONSHIPS BETWEEN THE PLASMA ENVIRONMENT AND THE COMPOSITION AND OPTICAL-PROPERTIES OF PLASMA-POLYMERIZED THIN-FILMS PRODUCED IN RF DISCHARGES OF C2H2-SF6 MIXTURES

Polymer films were grown in rf discharges containing different proportions of C2H2 and SF6. Quantitative optical emission spectrometry (actinometry) was used to follow the trends in the plasma concentrations of the species H and F, and more tentatively, of CH, CF, and CF2, as a function of the feed composition. Infrared spectroscopy revealed the density of CH and CF bonds in the deposited material. As the partial pressure of SF6 in the feed was increased, the degree of fluorination of the polymer also rose. The form of the dependency of the deposition rate on the proportion of SF6 in the feed was in good qualitative agreement with the activated growth model. From transmission ultraviolet visible spectroscopy data the refractive index and the absorption coefficient of the polymers were calculated as a function of the deposition parameters. Since the optical gap depended to some extent upon the degree of fluorination, it could, within limits, be determined by a suitable choice of the proportion of SF6 in the feed. A qualitative explanation of this relationship is given.

Effects of nitrogen ion irradiation on plasma polymerized films produced from titanium tetraiso pro poxide-oxygen-helium mixtures

In this work films were produced by the plasma enhanced chemical vapor deposition (PECVD) of titanium tetraisopropoxide-oxygen-helium mixtures and irradiated with 150 keV singly-charged nitrogen ions (N(+)) at fluences, phi, between 10(14) and 10(16) cm(-2). Irradiation resulted in compaction, which reached about 40% (measured via the film thickness) at the highest fluence. Infrared reflection-absorption spectroscopy (IRRAS) revealed the presence of Ti-O bonds in all films. Both O-H and C-H groups were present in the as-deposited films, but the density of each of these decreased with increasing phi and was absent at high phi, indicating a loss of hydrogen. X-ray photoelectron spectroscopy (XPS) analyses revealed an increase in the C to Ti atomic ratio as phi increased, while the O to Ti ratio hardly altered, remaining at around 2.8. The optical gap of the films, derived from data obtained by ultraviolet-visible spectroscopy (UVS), remained at about 3.6 eV for all fluences except the highest, for which an abrupt fall to around 1.0 eV was observed. For the irradiated films, the electrical conductivity, measured using the two-point method, showed a systematic increase with increasing phi. (c) 2008 Elsevier B.V. All rights reserved.