Dynamique sub-picoseconde de l'interaction laser de puissance – agrégats de gaz rare : émission intense de rayons X et production d'ions multichargés.

National audienceLors de campagnes d'expériences réalisées sur le Laser Ultra Court Accordable du CEA/Saclay, nous avons étudié le rayonnement X, tant qualitativement (spectroscopie et énergie moyenne des photons) que quantitativement (taux absolus et lois d'évolution), émis lors de l'interaction d'un jet effusif d'agrégats de gaz rare (Ar, Kr, Xe comprenant entre 10^4 et 10^6 atomes/agrégat) avec un laser femtoseconde de puissance (éclairement jusqu'à quelques 10^17 W/cm2). Les résultats présentés dans ce manuscrit sont uniquement dédiés aux agrégats d'Ar pour lesquels nous avons observé un rayonnement X issu d'ions fortement multichargés (jusqu'à l'Ar16+) présentant des lacunes en couches K. La technique de spectroscopie X utilisée a permis de déterminer pour la première fois des taux absolus ainsi que les lois d'évolution de l'émission X en fonction de l'ensemble des paramètres gouvernant l'interaction (intensité, polarisation, longueur d'onde et durée du pulse laser aussi bien que taille, densité et numéro atomique des agrégats)

A low power, low phase noise 10 GHz MIC oscillator

International audienceThis paper presents the design and the fabrication of a compact MIC 10 GHz single-transistor oscillator. It includes a packaged SiGe HBT (Infineon BFP740F) along with a low-Q coupled line resonator and only consumes 5 mA from a 3V power supply for an output power of -6 dBm. Its phase-noise has been measured at -117 dBc/Hz @100 kHz offset. Such performance is the result of a careful modeling process. The two most challenging aspects of the design were the stability analysis of the 10 GHz oscillator in hybrid technology and phase-noise optimization

Conception et Réalisation d'un Oscillateur Bande X à Très Faible Bruit de Phase

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MMIC Oscillator Phase Noise Measurement and Simulation using Experimental FET L.F. Noise Data and State of Art CAD Tools

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Relations of polarized scattering signatures observed by the TRMM Microwave Instrument with electrical processes in cloud systems.

International audienceThe polarized scattering signatures observed in convective cloud systems with the Tropical Rainfall Measuring Mission (TRMM) Microwave Instrument are analyzed. In particular, and in contrast to the positive polarization difference (TbV-TbH > 0) observed when scattering by large ice particles is important, we also find a negative polarization difference. Radiative transfer simulations show that such a polarization difference can be explained by relatively large, mostly vertically oriented, non-spherical particles but not by horizontally or randomly oriented non-spherical particles. We establish a relationship between the occurrence of the negative polarization difference signature and electrical activity in the cloud using coincident observations by the Lightning Imaging Sensor also on board TRMM. The negative polarization difference is thus related to non-spherical particles that are mostly vertically oriented as revealed by the lightning activity. This result confirms that a careful analysis of passive microwave observations over clouds provides valuable information about the cloud ice phase

Determining clustering properties through the selectivity of collision dynamics

International audienceBy exploiting the specific properties of cluster dynamics under the three types of ICPEAC ``projectiles'', i.e. electrons, intense femtosecond photon pulses and slow highly charged ions, we access to the temporal structure of the cluster bunch which give rise to a direct experimental measurement of the clustering rate

Development of precipitation retrievals at millimeter and sub-millimeter wavelenghts for geostationaly satellites.

International audienceWe study the potential of millimeter and sub-millimeter wavelengths for precipitation retrieval from geostationary sensors based on mesoscale cloud modeling and radiative transfer computation. Hydrometeor profiles simulated with the Meso-NH cloud resolving model for five European midlatitude situations are used to compute the brightness temperatures at frequencies from 23.8 to 875 GHz with the Atmospheric Transmission at Microwaves (ATM). Performances of both rain detection and rain rate retrieval are analyzed for different frequency sets, over ocean and land separately, and compared to the user requirements. The performances of a frequency set such as that already planned for geostationary satellites (with channels in the O2 lines at 50, 118, and 424 GHz, and in the H2O lines at 183, 325, 380 GHz) satisfy the requirements for Numerical Weather Prediction and NoWCasting in terms of rain detection as well as for rain rate retrieval above 1 mm/h. Suppressing the 50 GHz O2 channels does not seriously degrade the performances, except for rain rate below 1 mm/h, and, in addition, limits the spatial resolution problem from a geostationary orbit. Adding the thermal infrared observations has a limited impact. The retrieval of other hydrometeor quantities (cloud, ice) is also tested as well as the possibility to retrieve rain and the other hydrometeor profiles. These theoretical results are evaluated at close-to-millimeter wavelengths with coincident AMSU-B and radar observations (BALTEX and CAMRa). The results are degraded with respect to the theory, as expected, but are consistent with the observations

keV electron heating in laser-cluster interaction probed by X-ray and electron spectroscopy

International audienceThe interaction of intense laser pulses with nanoscopic rare-gas clusters provides a testing ground for laser-atom interaction at solid-state densities. We investigate the driven electronic dynamics on the femtosecond time scale both experimentally and theoretically using two complementary observables: the laser intensity dependence of characteristic X-ray emission and of high-energy (keV) electron spectra