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

The French Right-Wing Paradox – Maintaining the cordon sanitaire

In this article, we explain why the French mainstream right-wing party, today Les Républicains, has maintained until now a cordon sanitaire between itself and its far-right counterpart, the Rassemblement National. We examine the usual hypotheses identified by the literature on coalitions between mainstream and far-right parties, and confirm that they are not able to explain the French case. We argue that this paradox can be solved by re-evaluating some core ideological disagreements, as well as the importance of competence and credibility in the party image of the mainstream right, which we identify – discussing Panebianco's genetic model – as a result of its historical role of governmental, established party

Effect of input pulse chirp on nonlinear energy deposition and plasma excitation in water

We analyze numerically and experimentally the effect of the input pulse chirp on the nonlinear energy deposition from $5\ \mu$J fs-pulses at $800$ nm to water. Numerical results are also shown for pulses at $400$ nm, where linear losses are minimized, and for different focusing geometries. Input chirp is found to have a big impact on the deposited energy and on the plasma distribution around focus, thus providing a simple and effective mechanism to tune the electron density and energy deposition. We identify three relevant ways in which plasma features may be tuned.Comment: 9 pages, 7 figure

Phase-locking modes in a bidimensional network of coupled water jets

International audienceIn this paper, we investigate the dynamics of a bidimensional network of coupled water jets impinging from below on a water/air interface. For each jet, a transition is observed at a critical flow rate value for which the surface bump at the vertical of the jet starts oscillating at a well-defined frequency. We infer that this oscillatory mode is the materialization at the surface of a helical instability of the submerged laminar jet. When coupled together, the bidimensionai network of oscillators exhibits monoperiodic collective modes whose spatial arrangements are similar to those encountered in crystals. A collection of phase-locking modes is observed for each geometry, and stability diagrams are constructed. Analysis of the coupling between the jets reveals a long distance coupling through surface waves. A tuning criterion is proposed to explain the bifurcation from one mode to another. Finally, the symmetries of the system are investigated using two different systematic schemes. The predictions are compared with the observations and some features of the particular topology of phase-locking modes are explained

Laser beam self-symmetrization in air in the multifilamentation regime

We show experimental and numerical evidence of spontaneous self-symmetrization of focused laser beams experiencing multi-filamentation in air. The symmetrization effect is observed as the multiple filaments generated prior to focus approach the focal volume. This phenomenon is attributed to the nonlinear interactions amongst the different parts of the beam mediated by the optical Kerr effect, which leads to a symmetric redistribution of the wave vectors even when the beam consists of a bundle of many filaments.Comment: 9 pages, 7 figure

Fine control of terahertz radiation from filamentation by molecular lensing in air

International audienceWe demonstrate a method to control remotely the terahertz (THz) source in air based on the bifilamentation of femtosecond laser pulses. By fine tuning the time delay between the two pulses, a significant modulation of the THz intensity from bifilamentation is observed. The phenomenon is attributed to the molecule quantum lensing effect around the air molecule revival time, which changes the separation between the two neighboring plasma producing filaments

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