260 research outputs found
Etude expérimentale et simulations numériques des propriétés spectrales de lasers X pompés par excitation collisionnelle.
La caractĂ©risation spectrale dĂ©taillĂ©e des lasers XUV gĂ©nĂ©rĂ©s dans des plasmas est un enjeu important des projets actuels de dĂ©veloppement qui visent Ă augmenter la puissance crĂȘte de ces sources. En effet les propriĂ©tĂ©s spectrales de ces lasers conditionnent d'autres propriĂ©tĂ©s importantes, telle que la durĂ©e minimum accessible (limite de Fourier). La plus courte durĂ©e actuellement dĂ©montrĂ©e expĂ©rimentalement est de 1 picoseconde. La technique d'injection d'un plasma de laser XUV avec une impulsion femtoseconde de rayonnement harmonique d'ordre Ă©levĂ© offre des perspectives trĂšs prometteuses pour rĂ©duire la durĂ©e d'impulsion jusqu'Ă quelques 100 femtosecondes, pourvu que l'on sache maintenir une bande spectrale de gain suffisamment large.Les lasers XUV pompĂ©s par excitation collisionnelle dans des ions nĂ©onoĂŻdes et nickeloĂŻdes ont Ă©tĂ© dĂ©veloppĂ©s dans des plasmas chauds crĂ©Ă©s aussi bien par dĂ©charge Ă©lectrique rapide que par diffĂ©rents types de lasers de puissance. On a ainsi accĂšs Ă une large variĂ©tĂ© de sources lasers XUV, qui diffĂšrent par les caractĂ©ristiques du faisceau Ă©mis, mais aussi par les paramĂštres du plasma (densitĂ©, tempĂ©rature) dans la zone de gain. On peut donc s'attendre Ă des propriĂ©tĂ©s spectrales diffĂ©rentes. Le but du travail que nous prĂ©sentons est d'Ă©tudier les propriĂ©tĂ©s spectrales des diffĂ©rents types de lasers XUV collisionnels existants, et d'Ă©valuer leur capacitĂ© Ă amplifier des impulsions de durĂ©e infĂ©rieure Ă 1 picoseconde, dans un mode injectĂ©.La caractĂ©risation spectrale des lasers XUV est expĂ©rimentalement difficile parce que la rĂ©solution spectrale nĂ©cessaire ( / ~10-5) n'est pas accessible avec les meilleurs spectromĂštres actuels. Dans notre Ă©tude, nous avons atteint cette rĂ©solution en mesurant la cohĂ©rence temporelle de la source Ă l'aide d'un interfĂ©romĂštre Ă division de front d'onde, spĂ©cifiquement conçu pour ces mesures, Ă partir desquelles largeur spectrale peut ĂȘtre dĂ©duite.Nous avons caractĂ©risĂ© trois types de lasers XUV collisionnels, dĂ©veloppĂ©s dans trois laboratoires diffĂ©rents: pompage transitoire dans le molybdĂšne nickeloĂŻde, pompage par dĂ©charge Ă©lectrique dans l'argon nĂ©onoĂŻde et pompage quasi-stationnaire dans le zinc nĂ©onoĂŻde. Dans chaque cas la cohĂ©rence temporelle a Ă©tĂ© mesurĂ©e prĂ©cisĂ©ment. De plus nous avons Ă©tudiĂ© l'effet de la saturation de l'amplification et (pour le Ni-like Mo) l'influence du mode injectĂ©. Nous avons Ă©galement Ă©tudiĂ© le comportement temporel du laser transitoire Ni-like Mo Ă l'aide d'une camĂ©ra streak X ultra-rapide. Nos mesures spectrales sont comparĂ©es Ă des rĂ©sultats de simulations numĂ©riques prenant en compte les diffĂ©rents mĂ©canismes d'Ă©largissement ainsi que les effets de transfert radiatif. Nous avons Ă©tudiĂ© l'Ă©volution du profil spectral avec l'amplification et la saturation, et nous avons Ă©valuĂ© les limites de Fourier correspondantes.Le temps de cohĂ©rence le plus court (ie la largeur spectrale la plus grande) est mesurĂ© pour le laser XUV quasi-stationnaire, qui correspond au plasma qui a la plus forte densitĂ© et la plus forte tempĂ©rature ionique.Improving the knowledge of the spectral and temporal properties of plasma-based XUV lasers is an important issue for the ongoing development of these sources towards significantly higher peak power. The spectral properties of the XUV laser line actually control several physical quantities that are important for applications, such as the minimum duration that can be achieved (Fourier-transform limit). The shortest duration experimentally achieved to-date is ~1 picosecond. The demonstrated technique of seeding XUV laser plasmas with a coherent femtosecond pulse of high-order harmonic radiation opens new and promising prospects to reduce the duration to a few 100 fs, provided that the gain bandwidth can be kept large enough.XUV lasers pumped by collisional excitation of Ni-like and Ne-like ions have been developed worldwide in hot plasmas created either by fast electrical discharge, or by various types of high-power lasers. This leads to a variety of XUV laser sources with distinct output properties, but also markedly different plasma parameters (density, temperature) in the amplification zone. Hence different spectral properties are expected. The purpose of our work was then to investigate the spectral behaviour of the different types of existing collisional excitation XUV lasers, and to evaluate their potential to support amplification of pulses with duration below 1 ps in a seeded mode.The spectral characterization of plasma-based XUV lasers is challenging because the extremely narrow bandwidth (typically / ~10-5) lies beyond the resolution limit of existing spectrometers in this spectral range. In our work the narrow linewidth was resolved using a wavefront-division interferometer specifically designed to measure temporal coherence, from which the spectral linewidth is inferred. We have characterized three types of collisional XUV lasers, developed in three different laboratories: transient pumping in Ni-like Mo, capillary discharge pumping in Ne-like Ar and quasi-steady state pumping in Ne-like Zn. Besides the accurate measurement of the temporal coherence of the laser in each case, we have studied the spectral behaviour when the laser is operated in the saturation regime and (in Ni-like Mo) when it is seeded with high-order harmonic radiation. We have also investigated the temporal behaviour of the Ni-like Mo transient XUV laser, using an ultrafast X-ray streak camera. Our linewidth measurements are compared with detailed numerical calculations including relevant broadening mechanisms as well as radiative transfer effects. The evolution of the spectral profile with amplification and saturation was studied for different plasma parameters, and corresponding Fourier-transform limit duration were evaluated.The shortest temporal coherence (ie the largest bandwidth) is measured for the quasi-steady state pumping XUV laser, which operates at the highest density and ionic temperature.PARIS11-SCD-Bib. Ă©lectronique (914719901) / SudocSudocFranceF
A review of X-ray laser development at Rutherford Appleton Laboratory
Recent experiments undertaken at the Rutherford Appleton Laboratory to produce X-ray lasing over the 5-30 nm wavelength range are reviewed. The efficiency of lasing is optimized when the main pumping pulse interacts with a preformed plasma. Experiments using double 75-ps pulses and picosecond pulses superimposed on 300-ps background pulses are described. The use of travelling wave pumping with the approximately picosecond pulse experiments is necessary as the gain duration becomes comparable to the time for the X-ray laser pulse to propagate along the target length. Results from a model taking account of laser saturation and deviations from the speed of light c of the travelling wave and X-ray laser group velocity are presented. We show that X-ray laser pulses as short as 2-3 ps can be produced with optical pumping pulses of approximate to1-ps
Pulse-front tilt for short-wavelength lasing by means of traveling-wave plasma-excitation
Generation of coherent short-wavelength radiation across a plasma column is dramatically improved under traveling-wave excitation (TWE). The latter is optimized when its propagation is close to the speed of light, which implies small-angle target-irradiation. Yet, short-wavelength lasing needs large irradiation angles in order to increase the optical penetration of the pump into the plasma core. Pulse-front back-tilt is considered to overcome such trade-off. In fact, the TWE speed depends on the pulse-front slope (envelope of amplitude), whereas the optical penetration depth depends on the wave-front slope (envelope of phase). Pulse-front tilt by means of compressor misalignment was found effective only if coupled with a high-magnification front-end imaging/focusing component. It is concluded that speed matching should be accomplished with minimal compressor misalignment and maximal imaging magnification
SOLORZANO, ĂNGELES Y ROSARIO [Material grĂĄfico]
Copia digital. Madrid : Ministerio de EducaciĂłn, Cultura y Deporte, 201
IgG4-Related Sclerosing Disease, an Emerging Entity: A Review of a Multi-System Disease
Immunoglobulin G4-related systemic disease (IgG4-RSD) is a recently defined emerging entity characterized by a diffuse or mass forming inflammatory reaction rich in IgG4-positive plasma cells associated with fibrosclerosis and obliterative phlebitis. IgG4-RSD usually affects middle aged and elderly patients, with a male predominance. It is associated with an elevated serum titer of IgG4, which acts as a marker for this recently characterized entity. The prototype is IgG4-related sclerosing pancreatitis or autoimmune pancreatitis (AIP). Other common sites of involvement are the hepatobiliary tract, salivary gland, orbit, and lymph node, however practically any organ can be involved, including upper aerodigestive tract, lung, aorta, mediastinum, retroperitoneum, soft tissue, skin, central nervous system, breast, kidney, and prostate. Fever or constitutional symptoms usually do not comprise part of the clinical picture. Laboratory findings detected include raised serum globulin, IgG and IgG4. An association with autoantibody detection (such as antinuclear antibodies and rheumatoid factor) is seen in some cases. Steroid therapy comprises the mainstay of treatment. Disease progression with involvement of multiple organ-sites may be encountered in a subset of cases and may follow a relapsing-remitting course. The principal histopathologic findings in several extranodal sites include lymphoplasmacytic infiltration, lymphoid follicle formation, sclerosis and obliterative phlebitis, along with atrophy and destruction of tissues. Immunohistochemical staining shows increased IgG4+ cells in the involved tissues (>50 per high-power field, with IgG4/IgG ratio >40%). IgG4-RSD may potentially be rarely associated with the development of lymphoma and carcinoma. However, the nature and pathogenesis of IgG4-RSD are yet to be fully elucidated and provide immense scope for further studies
Low incidence of SARS-CoV-2, risk factors of mortality and the course of illness in the French national cohort of dialysis patients
Pressure Ionization and Line Merging in Strongly Coupled Plasmas Produced by 100-fs Laser Pulses
Absorption positive et negative de rayonnement X-UV dans les plasmas denses : etude des populations de niveaux ioniques, inversions de populations
SIGLECNRS T 56015 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc
- âŠ