Plasma dynamics of a laser filamentation-guided spark

International audienceWe investigate experimentally the plasma dynamics of a centimeter-scale, laser filamentation-guided spark discharge. Using electrical and optical diagnostics to study monopolar discharges with varying current pulses we show that plasma decay is dominated by free electron recombination if the current decay time is shorter than the recombination characteristic time. In the opposite case, the plasma electron density closely follows the current evolution. We demonstrate that this criterion holds true in the case of damped AC sparks, and that alternative current is the best option to achieve a long plasma lifetime for a given peak current

Superfilamentation in air

The interaction between a large number of laser filaments brought together using weak external focusing leads to the emergence of few filamentary structures reminiscent of standard filaments, but carrying a higher intensity. The resulting plasma is measured to be one order of magnitude denser than for short-scale filaments. This new propagation regime is dubbed superfilamentation. Numerical simulations of a nonlinear envelope equation provide good agreement with experiments.Comment: 5 pages, 4 figure

Underwater acoustic wave generation by filamentation of terawatt ultrashort laser pulses

Acoustic signals generated by filamentation of ultrashort TW laser pulses in water are characterized experimentally. Measurements reveal a strong influence of input pulse duration on the shape and intensity of the acoustic wave. Numerical simulations of the laser pulse nonlinear propagation and the subsequent water hydrodynamics and acoustic wave generation show that the strong acoustic emission is related to the mechanism of superfilamention in water. The elongated shape of the plasma volume where energy is deposited drives the far-field profile of the acoustic signal, which takes the form of a radially directed pressure wave with a single oscillation and a very broad spectrum.Comment: 9 pages, 12 figure

Two-color interferometer for the study of laser filamentation triggered electric discharges in air

International audienceWe present a space and time resolved interferometric plasma diagnostic for use on plasmas where neutral-bound electron contribution to the refractive index cannot be neglected. By recording simultaneously the plasma optical index at 532 and 1064 nm, we are able to extract independently the neutral and free electron density profiles. We report a phase resolution of 30 mrad, corresponding to a maximum resolution on the order of 4 × 10 22 m −3 for the electron density, and of 10 24 m −3 for the neutral density. The interferometer is demonstrated on centimeter-scale sparks triggered by laser filamentation in air with typical currents of a few tens of A

Utilisation d'une source laser pulsée à haute energie comme source acoustique large bande en milieu liquide Source acoustique générée par un laser pulsé intense

International audienceIn this work the non-linear opto-acoustic problem which consists in generating an acoustic signal in water from an intense ultra short laser pulse has been studied. The acoustic source obtained could be related to the phenomenon of filamentation which produces a contraction of the initial beam accompanied by the formation of plasma. Relatively recent work has shown that lasers of this type could be used to produce remote acoustic sources with interesting applications to underwater acoustics. The spectrum of the sound source obtained was investigated and its directivity pattern in both planes (plane of the filament and plane 96 TS. Volume 33 – n° 1/2016 perpendicular to the filament) was measured. The sound level of the source as a function of energy, duration, and wavelength of the laser pulse was also measured.Ce travail est relatif à l'étude expérimentale d'un problème d'opto-acoustique non linéaire, consistant à générer un signal acoustique dans l'eau à partir d'un laser pulsé térawatt (TW). La source acoustique obtenue a pu être reliée au phénomène de filamentation qui produit une contraction du faisceau initial, accompagnée de la formation d'un plasma. Des travaux relativement récents ont montré que les lasers de ce type pouvaient être utilisés pour produire des sources acoustiques déportées, avec des applications intéressantes pour l'acoustique sous-marine. Le spectre de la source acoustique obtenue a été étudié à l'aide de plusieurs hydrophones couvrant une très large bande de fréquence, et le diagramme de directivité a été mesuré dans deux plans (plan du filament et plan perpendiculaire au filament). Le niveau acoustique de la source en fonction de l'énergie, de la durée, et de la longueur d'onde de l'impulsion laser, a également été étudi

Motrial, first search engine in clinical trial on non pharmaceutical interventions (NPIs)

Le nombre de publications d’études cliniques évaluant les interventions non médicamenteuses (INM) augmente exponentiellement depuis 2000. Il encourage les chercheurs à réaliser les revues systématiques et les méta-analyses attendues par les professionnels de santé, les patients et les décideurs pour connaître leur efficacité réelle et leur indication pertinente. Seulement, la diversification des supports de communication médicale et scientifique, les stratégies opportunistes de publication, les informations manquantes dans les publications et la non exhaustivité des bases de données biomédicales rendent la recherche bibliographique complexe et à risque de biais. Pour répondre à ce manque, la Plateforme CEPS propose un moteur de recherche, appelé Motrial, qui permet de collecter, de trier et d’organiser les publications d’études cliniques sur les INM.The number of clinical trial publications assessing non-pharmacological intervention (NPI) has been increasing exponentially since 2000. It encourages researchers to carry out the systematic reviews and meta-analyzes expected by health professionals, patients, and decision-makers to learn about their real effectiveness and their relevant indication. However, the diversification of medical and scientific communication media, opportunistic publishing strategies, missing data in publications and non-exhaustiveness of biomedical databases make bibliographic research complex and at risk of bias. To address this shortcoming, the academic Plateforme CEPS offers a search engine, called Motrial, that collects, sorts and organizes publications of NPI clinical trials

Triggering, guiding and deviation of long air spark discharges with femtosecond laser filament

International audienceIn the perspective of the laser lightning rod, the ability of femtosecond filaments to trigger and to guide large scale discharges has been studied for several years. The present paper reports recent experimental results showing for the first time that filaments are able not only to trigger and guide but also to divert an electric discharge from its normal path. Laser filaments are also able to divert the spark without contact between laser and electrodes at large distance from the laser. A comparison between negative and positive discharge polarities also reveals important discrepancies in the guiding mechanism

Drug use for gastrointestinal symptoms during pregnancy: A French nationwide study 2010-2018.

PurposeTo describe drug prescription for gastrointestinal symptoms during pregnancy.MethodsUsing the French national health database, we identified pregnancies ending with a birth between April 2010 and December 2018, in France. We studied prescription of antacids, antispasmodics, antinauseants, laxatives and antidiarrheals during pregnancy, between two trimesters before and two trimesters after delivery. We also assessed hospitalization for gastrointestinal symptoms during pregnancy.ResultsAmong 6,365,471 pregnancies, 4,452,779 (74.0%) received at least one gastrointestinal drug during pregnancy; 2,228,275 (37.0%) received an antacid, 3,096,858 (51.5%) an antispasmodic, 1,861,731 (31.0%) an antinauseant, 919,116 (15.3%) a laxative and 617,808 (10.3%) an antidiarrheal. Prescription of proton pump inhibitors doubled from 12.2% in 2010 to 26.0% in 2018, while domperidone use decreased from 18.3% in 2010 to 2.2% in 2018. In addition, prescription of antacids increased from 7.0% during the trimester before pregnancy to 11.8% during the 1st trimester, 17.0% during the 2nd trimester and 23.4% during the 3rd trimester. Antispasmodic use was 10.6% during the trimester before pregnancy, 23.1% during the 1st trimester, 25.2% during the 2nd trimester and 24.0% during the 3rd trimester. Prescription of antinauseant drugs increased from 5.0% during the trimester before pregnancy to 25.7% during the 1st trimester, then decreased to 6.4% during the 2nd trimester and 3.2% during the 3rd trimester. Nausea/vomiting was the most common cause of hospitalization for gastrointestinal symptoms or diseases during pregnancy, although it accounted for only 1.0% of pregnancies.ConclusionsApproximately three-quarters of women use drugs for gastrointestinal symptoms during pregnancy in France. Prescription of gastrointestinal drugs during pregnancy should be the subject of more detailed risk-benefit assessment and recommendations

Evolution of a laser filamentation triggered electric discharge in air

International audienceSummary form only given. Laser filamentation guided electric discharges have many interesting applications, among which are the laser lightning rod, plasma aerodynamic control, high-power closing switches and plasma antennas. The latter cases rely on a precise control of the discharge plasma lifetime, either to adapt the switch or antenna on-state time to the current situation. In this work, we study the link between the temporal evolution of a laser filamentation triggered discharge plasma column and the discharge current waveform. The centimeter long plasma is generated by the discharge of a 2 nF capacitor charged to 15 kV, yielding a constant electric energy of 200 mJ. Various ballast resistances ranging from 400 to 10 Ω allow modifying the current waveform in the monopolar regime. A 29 μH coil can also be used to bring the circuit in the oscillatory regime. Plasma is characterized by means of two-color interferometry, enabling us to extract space and time-resolved electron density and neutral density radial profiles. We found that, in the monopolar regime, as the current pulse amplifies and shortens, electron density decay becomes dominated by electron-ion recombination, while low-current impulses result in a plasma decay closely related to the current waveform. Longer plasma lifetime is achieved using strong and short current pulses. As for the oscillatory regime, we show that in this case the plasma has a very slow decay, resulting in more favorable conditions for the generation of long lived plasma columns