Investigation of the Potential of Low Salinity Water Flooding as a Tertiary Process in Forties Sandstone Formation Fields

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Energy deposition from focused terawatt laser pulses in air undergoing multifilamentation

Laser filamentation is responsible for the deposition of a significant part of the laser pulse energy in the propagation medium. We found that using terawatt laser pulses and relatively tight focusing conditions in air, resulting in a bundle of co-propagating multifilaments, more than 60 % of the pulses energy is transferred to the medium, eventually degrading into heat. This results in a strong hydrodynamic reaction of air with the generation of shock waves and associated underdense channels for each short-scale filament. In the focal zone, where filaments are close to each other, these discrete channels eventually merge to form a single cylindrical low-density tube over a $\sim 1 \mu\mathrm{s}$ timescale. We measured the maximum lineic deposited energy to be more than 1 J/m.Comment: 7 pages, 7 figure

Dépôt d’énergie dans l’air par filamentation laser femtoseconde pour le contrôle des décharges électriques haute-tension

Laser filamentation is a spectacular optical propagation regime appearing for pulses of which peak power exceeds a few GW in air. Filament forms due to the optical Kerr effect, which tends to self-focus the beam until intensity reaches the medium ionization threshold by multiphoton absorption. A complex dynamic competition is then established between the Kerr effect on the one hand, and diffraction, nonlinear absorption and plasma defocusing effect on the other hand. This results in a reorganization of the beam profile, characterized by a thin (100 µm) and intense(10^18 W/m²) core able to propagate over a distance much longer than the Rayleigh length. When the initial pulse peak power largely exceeds filamentation threshold, several co-propagating filaments are formed in the same beam, with each of these multifilaments sharing physical properties of isolated single filaments. While propagating in air, filaments transfer a portion of the laser energy to the medium, mainly through Raman rotational excitation of air molecules, ionization and inverse Bremsstrahlung in the plasma. This energy is redistributed in one nanosecondand almost entirely converted into air molecule translational energy, that is heat. The medium reacts to this rapid heating by launching a cylindrical pressure wave that brings the system back to pressure equilibrium by ejecting matter from the center. This results in the formation of a hot underdense air channel, which slowly resorbs by diffusion at timescales > 1 ms. My work as a Ph. D. student first focused on the study and the optimization of laser energy deposition in air by filamentation. Thus, I investigated the influence of laser parameters such as pulse energy,focusing strength or pulse duration on deposited energy. To this purpose, I used several complementary diagnostics: study of pressure waves using microphones, characterization of the filamentation plasma by means of spectroscopy and time resolved study of underdense air channels using interferometry. I demonstrated in the single filamentation regime that above a given pulse energy, energy deposition becomes so important that the medium generates a shock wave instead of a sound wave, and that underdense channels can last for more than 100 ms. I also studied andcharacterized the high energy multifilamentation regime, showing that moderately focusing the pulse leads to a reorganization of filaments in the focal zone, generating large structures with a resulting plasma ten times denser than filaments. Filamentation-induced hydrodynamic effects lead to a transient reduction of the air breakdown voltage along the path of the laser pulse, enabling one to trigger and guide electric discharges. The second part of my thesis focused on the study and the optimization of such guided discharges for the design of a radio-frequency plasma antenna,contactless high-voltage switches or a laser lightning rod. To this purpose I developed and built an interferometric plasma diagnostic, allowing to measure the lifetime of generated plasmas. I also contributed to the proof of principle for a filament induced plasma antenna emitting RF signal. Finally, I took part to prospective experimental studies for the development of a laser lightning rod.La filamentation laser est un régime de propagation optique spectaculaire atteint pour des impulsions dont la puissance crête excède quelques gigawatts dans l’air. Le filament se forme sous l’action de l’effet Kerr optique du milieu traversé qui tend à auto-focaliser le faisceau jusqu’à ce que l’intensité résultante atteigne le seuil d’ionisation du milieu par absorption multiphotonique. Une compétition dynamique complexe s’établit alors entre l’effet Kerr, d’une part, et la diffraction, l’absorption non-linéaire de l’énergie laser et l’effet défocalisant du plasma d’autre part. Il en résulte une réorganisation du profil du faisceau, caractérisée par un coeur mince (100 µm) et intense (10^18 W/m²) pouvant se maintenir sur une distance égale à plusieurs longueurs de Rayleigh. Lorsque la puissance initiale de l’impulsion dépasse largement le seuil de filamentation, on assiste à la formation de plusieurs filaments co-propagatifs au sein du même faisceau, chacun de ces multifilaments possédant des caractéristiques physiques proches de monofilaments isolés. Au cours de sa propagation dans l’air, le filament transfère une partie de l’énergie laser au milieu, principalement via l’excitation rotationnelle Raman des molécules d’air, l’ionisation de l’air et l’effet deBremsstrahlung inverse au sein du plasma. Cette énergie est redistribuée au cours de la nanoseconde suivant le passage du laser, principalement sous forme d’énergie translationnelle des molécules d’air, c’est-à-dire de chaleur. Le milieu réagit à ce chauffage rapide par la formation d’une onde de pression cylindrique, qui ramène le système à l’équilibre de pression en éjectant de la matière du centre. Il en résulte la formation d’un canal d’air sous-dense et chaud, qui se résorbe par diffusion à des échelles de temps supérieures à la milliseconde. Ma thèse s’est en premier lieu focalisée sur l’étude et l’optimisation du dépôt d’énergie dans l’air par filamentation. J’ai ainsi étudié l’influencedes différents paramètres laser, comme l’énergie de l’impulsion, la focalisation employée et la durée d’impulsion sur la densité d’énergie déposée. Pour ce faire, j’ai employé plusieurs diagnostics complémentaires : mesure des ondes de pression à l’aide de microphones, analyse du plasma de filament par spectroscopie et mesure résolue en temps des canaux sous-dense par interférométrie. J’ai ainsi montré en régime de monofilamentation qu’au-delà d’une certaine énergie laser initiale, le dépôt d’énergie devient si important qu’une onde de choc est générée en lieu et place d’une onde sonore, et que les canaux sous-denses résultant ont des durées de vie de l’ordre de 100 ms. J’aiégalement étudié et caractérisé le régime de multifilamentation à haute énergie, montrant qu’en focalisant modérément l’impulsion, les filaments se réorganisent dans la zone focale pour former des structures plus larges générant un plasma dix fois plus dense que les filaments. Les effets hydrodynamiques engendrés par filamentation entraînent un abaissement transitoire du seuil de claquage électrique de l’air le long du trajet de l’impulsion laser, permettant ainsi de déclencher et de guider des décharges électriques. La seconde partie de ma thèse avait pour objet l’étude et l’optimisation de telles décharges guidées pour la mise au point d’une antenne plasma radio-fréquence, de commutateurs haute tension sans contact ou encore d’un paratonnerre laser. Pour ce faire, j’ai développé et construit un diagnostic plasma interférométrique à deux couleurs permettant de caractériser ladurée de vie des plasmas générés. J’ai également participé à une expérience de principe démontrant la possibilité de réaliser une antenne plasma RF à partir d’un filament laser. Enfin, j’ai participé à diverses études expérimentales prospectives dans l’optique du développement d’un paratonnerre laser

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

Self-seeded lasing in ionized air pumped by 800 nm femtosecond laser pulses

We report on the lasing in air and pure nitrogen gas pumped by a single 800 nm femtosecond laser pulse. Depending on gas pressure, incident laser power and beam convergence, different lasing lines are observed in the forward direction with rapid change of their relative intensities. The lines are attributed to transitions between vibrational and rotational levels of the first negative band of the singly charged nitrogen molecule-ion. We show that self-seeding plays an important role in the observed intensity changes.Comment: 9 pages, 4 figure

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

Lasing of ambient air with microjoule pulse energy pumped by a multi terawatt IR femtosecond laser

We report on the lasing action of atmospheric air pumped by an 800 nm femtosecond laser pulse with peak power up to 4 TW. Lasing emission at 428 nm increases rapidly over a small range of pump laser power, followed by saturation above ~ 1.5 TW. The maximum lasing pulse energy is measured to be 2.6 uJ corresponding to an emission power in the MW range, while a maximum conversion efficiency of is measured at moderate pump pulse energy. The optical gain inside the filament plasma is estimated to be excess of 0.7/cm. The lasing emission shows a doughnut profile, reflecting the spatial distribution of the pump-generated white-light continuum that acts as a seed for the lasing. We attribute the pronounced saturation to the defocusing of the seed in the plasma amplifying region and to the saturation of the seed intensity

Study of filamentation with a high power high repetition rate ps laser at 1.03 µm

International audienceWe study the propagation of intense, high repetition rate laser pulses of picosecond duration at 1.03 µm central wavelength through air. Evidence of filamentation is obtained from measurements of the beam profile as a function of distance, from photoemission imaging and from spatially resolved sonometric recordings. Good agreement is found with numerical simulations. Simulations reveal an important self shortening of the pulse duration, suggesting that laser pulses with few optical cycles could be obtained via double filamentation. An important lowering of the voltage required to induce guided electric discharges between charged electrodes is measured at high laser pulse repetition rate.-repetition-rate picosecond pump laser based on a Yb:YAG disk amplifier for optical parametric amplification

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

Integrated immunovirological profiling validates plasma SARS-CoV-2 RNA as an early predictor of COVID-19 mortality.

peer reviewedDespite advances in COVID-19 management, identifying patients evolving toward death remains challenging. To identify early predictors of mortality within 60 days of symptom onset (DSO), we performed immunovirological assessments on plasma from 279 individuals. On samples collected at DSO11 in a discovery cohort, high severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) viral RNA (vRNA), low receptor binding domain–specific immunoglobulin G and antibody-dependent cellular cytotoxicity, and elevated cytokines and tissue injury markers were strongly associated with mortality, including in patients on mechanical ventilation. A three-variable model of vRNA, with predefined adjustment by age and sex, robustly identified patients with fatal outcome (adjusted hazard ratio for log-transformed vRNA = 3.5). This model remained robust in independent validation and confirmation cohorts. Since plasma vRNA’s predictive accuracy was maintained at earlier time points, its quantitation can help us understand disease heterogeneity and identify patients who may benefit from new therapies