Three-dimensional Maxwell-Bloch calculation of the temporal profile of a seeded soft x-ray laser pulse

International audienceWe present three-dimensional modeling of amplification of a high-order harmonic seed by a soft x-ray laser plasma. The time-dependent evolution of the x-ray signal is determined from a fully dynamic Maxwell-Bloch calculation. At high seed intensities , a simplified one-dimensional calculation leads to strong Rabi-like temporal oscillations of the output signal. However, such oscillations have not been observed experimentally. Our three-dimensional calculations demonstrate that this is due to spatial non-uniformities in the plasma gain that cause the Rabi oscillations to dampen dramatically. Large amplitude Rabi-like oscillations are expected to appear only in long and uniform plasma. Such targets require optimized guiding techniques

A proposal for multi-tens of GW fully coherent femtosecond soft X-ray lasers

X-ray free-electron lasers1,2 delivering up to 131013 coherent photons in femtosecond pulses are bringing about a revolution in X-ray science3?5. However, some plasma-based soft X-ray lasers6 are attractive because they spontaneously emit an even higher number of photons (131015), but these are emitted in incoherent and long (hundreds of picoseconds) pulses7 as a consequence of the amplification of stochastic incoherent self-emission. Previous experimental attempts to seed such amplifiers with coherent femtosecond soft X-rays resulted in as yet unexplained weak amplification of the seed and strong amplification of incoherent spontaneous emission8. Using a time-dependent Maxwell?Bloch model describing the amplification of both coherent and incoherent soft X-rays in plasma, we explain the observed inefficiency and propose a new amplification scheme based on the seeding of stretched high harmonics using a transposition of chirped pulse amplification to soft X-rays. This scheme is able to deliver 531014 fully coherent soft X-ray photons in 200 fs pulses and with a peak power of 20 GW

Modelling of the double pass X-ray laser effects on its focalisation

In this paper we describe a new ray trace code. This code is a three dimensional description of beam propagation, including half cavity mirror. It is based on the integration of the ray equation and on the calculation of the intensity along the plasma. It works as a post-processor of the hydrodynamic/atomic code " EHYBRID ", which calculates the time evolution of the gain, the emissivity, the electronic density and the width of the plasma. We will present results obtained on different schemes of x-ray laser generation

Sources X et XUV intenses et brèves : Journées d'Orsay des 5 et 6 mars 1998

L'idée de ces journées est née du besoin de coordonner les efforts des équipes travaillant sur les nouvelles sources X et XUV intenses et brèves. Ces sources, qui arrivent maintenant à maturité, commencent à offrir des possibilités nouvelles d'applications pour de nombreux domaines de recherche. Il a paru nécessaire de faire le point des résultats obtenus récemment à la fois sur les sources et sur leurs applications, afin de lancer une prospective et de rechercher les moyens d'organiser cette communauté scientifique, harmoniser les programmes et rationaliser l'utilisation des moyens. Une question particulièrement importante et difficile a été révélée avec force au cours de ces journées. Il s'agit des besoins en optique multicouche, qui sont presque exclusivement satisfaits par des laboratoires de recherche qui ne peuvent consacrer qu'une part marginale de leur activité à cette production. En revanche, le marché est actuellement trop faible pour être pris en charge par les entreprises à un prix compatibles avec les moyens de la recherche publique. Le recueil des exposés présentés au cours de ces journées sera publié prochainement par l'université Paris-Su

Optimization of the focused flux of high harmonics

Following the theoretical predictions [1], the observation of two-photon processes by interaction of vacuum ultraviolet (VUV) radiation with inner-shell levels of atoms requires focused intensities in the $10^{13}{-}10^{14}$ W/cm2 range. Our aim is to reach this regime in order to study non-linear optics at these wavelengths. We first optimized the high harmonic conversion efficiency in argon by studying the best experimental conditions for phase-matching, concentrating on focus geometry related to laser energy, cell length and position relative to the focus. We then studied the resulting harmonic beam focusability by a toroidal mirror (f=10 cm) and made an image of the harmonic focus. We conclude with an evaluation of the focused intensity that we are able to reach experimentally

Sequential pumping in Ne-like iron. Multiple irradiation of X-ray lasers

We study a X-ray laser (XRL) pumped by two 140 ps pulses frorn an IR laser beam. With the aim to regenerate the plasma gain with the second pulse, and then realise a double pass, we separate the two pulses by 800 ps. First experimental results obtained at LULI with Ne-like iron were very encouraging. In single pass mode, two saturated X-ray laser emissions have been observed with reproducible way. The gain values were respectively 15 cm-1 and 12 cm-1. This result qualitatively agrees with EHYBRID and Maxwell-Bloch modelling. We present the first far field pattern obtained in Ne-like iron and we deduce the two different positions of each XRL beam by subtracting images

Method of time resolved refractive index measurements of x-ray laser heated solids

International audienceWith the advent of new x-ray light-sources worldwide, the creation of dense, uniformly heated plasma states arising from intense x-ray irradiation of solids has been made possible. In the early stages of x-ray solid heating, before significant hydrodynamic motion occurs, the matter exists in a highly non-equilibrium state. A method based on wavefront sensing is proposed to probe some of the fundamental properties of these states. The deflection and absorption of a high harmonic probe beam propagated through the plasma can be measured with a wavefront sensor, and allow for the determination of the complex refractive index (RI) of the plasma, giving a 2D map of the optical properties as function of time in a pump-probe arrangement. A solid heating model has been used to estimate the expected temperatures of x-ray heated thin foils, and these temperatures are used in three separate models to estimate the changes in the refractive index. The calculations show the changes induced on an extreme ultra-violet (XUV) probe beam by a solid density thin foil plasma are significant, in terms of deflection angle and absorption, to be measured by already existing XUV Hartmann wavefront sensors. The method is applicable to a wide range of photon energies in the XUV (10s to several 100s of eV) and plasma parameters, and can add much needed experimental data to the fundamental properties of such dense plasma states. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4794964

LASERIX : une station de travail ouverte pour l'étude et l'utilisation de lasers de 10 à 40 nm de longueur d'onde

Les lasers à rayons X sont les sources les plus brillantes actuellement disponibles dans une gamme de longueurs d'onde comprises entre 10 et 40 nm. Leurs propriétés permettent de réaliser des expériences inconcevables auparavant. Le développement des applications des lasers X implique la réalisation de stations de travail spécifiquement destinées à la production et à l'utilisation de lasers X. “LASERIX” est un projet de l'Université Paris-Sud qui sera construit dans les locaux de l'ENSTA à Palaiseau. Cette installation servira au développement des applications des lasers X, à l'amélioration de propriétés optiques des lasers X existants et à la réalisation de nouveaux lasers X. Elle sera ouverte aux équipes utilisatrices sélectionnées par un comité de programme