Large-scale doming on Europa: A model of formation of Thera Macula.

International audienceSince Galileo spacecraft reveals Europa's surface at high and medium resolutions, deformation and processes affecting the relatively young surface have been more accurately defined. This work reports the observations carried out on a large-scale feature of the south hemisphere, Thera Macula. It is shown that Thera presents common points with many other features including small-scale domes, lenticulae and large-scale chaotic areas (disrupted ancient surfaces lying on a dark matrix), but remains singular through its asymmetric morphology. On the basis of observations, we propose a scenario for the setting of Thera Macula. It involves a large-scale doming (40–70km in radius) of the pre-existing surface associated with ductile deformations, and the consecutive collapse of the created megadome associated with brittle disruption of blocks and flow of low viscosity material over the surrounding ridged plains. The processes responsible for each stage of the proposed scenario have been investigated. Both cryomagmatic and diapiric origins are discussed and confronted by observations. Finally, comparison of similar features at various scales suggests that Thera Macula by its originalities (asymmetry, rounding bulge) may have preserved the intermediate stages of the formation of subcircular chaos at least up to about 50km in radius. A common evolution and endogenic origin for multi-scale hot spot features is proposed: (1) the doming stage, (2) the collapse and extrusion stage and (3) the relaxation stage

Les structures d'impact sur Europe : implications sur la rhéologie et la thermique de la croûte de glace. Impact features on Europa : rheological and thermal states of the icy crust.

texte intégral en français English abridged versionInternational audienceThe depth of the brittle/ductile transition has been estimated under each graben rounding two ancient impact basins on Europa, Callanish and Tyre. Surface thermal gradients have been computed and are respectively equal to 4.3 +/- 0.4 and 2.4 +/- 0.25 K/km. These results differ strongly from previous works obtained on other Europa's features. This can be explained by the variation of both the icy grain size and the chemical composition of the crust, but also by the variation of the local deformation rate

Seeded attosecond-pulse generation in structured media: A road for attosecond optics

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Génération d'impulsions attosecondes isolées

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Compact 60fs multigigawatt diode-pumped laser using postcompression technique

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High order harmonic generation at ultra high repetition rate from ytterbium doped fiber chirped pulse amplification

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Comparison of two spatial characterisation methods of XUV high-order harmonics for spatio-temporal control of attosecond pulses

International audienceExtreme ultraviolet (XUV) sources (10–100 nm) based upon high harmonic generation (HHG) in gases emit attosecond pulses and exhibit a high spatial and temporal coherence useful for a great range of applications. To further develop applications, it is very important to control the focusing of XUV beams as well as the evolution of the attosecond pulse duration during propagation. It has been demonstrated that the spatial profile of high harmonics strongly depends on the harmonic order [1] which consequently introduces chromatic aberrations at XUV focus and subsequent inhomogeneities in the attosecond temporal profile [2]. Nevertheless, the spatial properties of the XUV beam can be controlled to some extend [3], [4] in order to make it more homogeneous thus improving the spatio-temporal properties. To that respect retrieving the front phase of the XUV beam becomes essential. We will show two techniques to experimentally extract the front-phase

High-order harmonic generation at a megahertz-level repetition rate directly driven by an ytterbium-doped-fiber chirped-pulse amplification system

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