A parametric study

Based on both static (extended Köhler) and dynamic modelling, we investigate the influence of temperature,humidity, HNO3 initial concentration, as well as of the particle concentration, on the efficiency of HNO3-mediated laser- induced condensation. This mechanism is most efficient for low temperatures, high HNO3 concentration, and relative humidities. It is, however, still active up to 30 °C, down to 70% relative humidity, and below the ppm level of HNO3. Furthermore, lower particle concentration minimizing the depletion of both HNO3 and water vapor is more favourable to particle growth

Saturation of the filament density of ultrashort intense laser pulses in air

We experimentally and numerically characterize multiple filamentation of laser pulses with incident intensities of a few TW/cm2. Propagating 100TW laser pulses over 42m in air, we observe a new propagation regime where the filament density saturates. As also evidenced by numerical simulations in the same intensity range, the total number of filaments is governed by geometric constraints and mutual interactions among filaments rather than by the available power in the bea

On negative higher-order Kerr effect and filamentation

As a contribution to the ongoing controversy about the role of higher-order Kerr effect (HOKE) in laser filamentation, we first provide thorough details about the protocol that has been employed to infer the HOKE indices from the experiment. Next, we discuss potential sources of artifact in the experimental measurements of these terms and show that neither the value of the observed birefringence, nor its inversion, nor the intensity at which it is observed, appear to be flawed. Furthermore, we argue that, independently on our values, the principle of including HOKE is straightforward. Due to the different temporal and spectral dynamics, the respective efficiency of defocusing by the plasma and by the HOKE is expected to depend substantially on both incident wavelength and pulse duration. The discussion should therefore focus on defining the conditions where each filamentation regime dominates.Comment: 22 pages, 11 figures. Submitted to Laser physics as proceedings of the Laser Physics 2010 conferenc

Progress towards lightning control using lasers

Lightning research needs on-demand lightning strikes, because of the random character of natural lightning. Lasers have been proposed as alternatives to the current technique using rocket-pulled wires, because they would expectedly provide more flexibility. However, high-energy, nanosecond lasers cannot provide long connected plasma channels. In contrast, we recently reported the triggering of electric events in thunderclouds using ultrashort laser pulses. Further improvements of the laser pulse sequence and experiment geometry are discussed

Field measurements suggest the mechanism of laser-assisted water condensation

Because of the potential impact on agriculture and other key human activities, efforts have been dedicated to the local control of precipitation. The most common approach consists of dispersing small particles of dry ice, silver iodide, or other salts in the atmosphere. Here we show, using field experiments conducted under various atmospheric conditions, that laser filaments can induce water condensation and fast droplet growth up to several μm in diameter in the atmosphere as soon as the relative humidity exceeds 70%. We propose that this effect relies mainly on photochemical formation of p.p.m.-range concentrations of hygroscopic HNO3, allowing efficient binary HNO3–H2O condensation in the laser filaments. Thermodynamic, as well as kinetic, numerical modelling based on this scenario semiquantitatively reproduces the experimental results, suggesting that particle stabilization by HNO3 has a substantial role in the laser-induced condensation

Modelling of HNO₃-mediated laser-induced condensation: A parametric study

Based on both static (extended Köhler) and dynamic modelling, we investigate the influence of temperature,humidity, HNO3 initial concentration, as well as of the particle concentration, on the efficiency of HNO3-mediated laser-induced condensation. This mechanism is most efficient for low temperatures, high HNO3 concentration, and relative humidities. It is, however, still active up to 30 °C, down to 70% relative humidity, and below the ppm level of HNO3. Furthermore, lower particle concentration minimizing the depletion of both HNO3 and water vapor is more favourable to particle growt

Laser-assisted water condensation in the atmosphere: a step towards modulating precipitation?

We review the recent results about laser-induced condensation based on self-guided filaments generated by ultrashort laser pulses. After recalling the physico-chemistry of cloud particle formation in the atmosphere and the physics of laser filamentation, we discuss experimental results on laser-induced condensation and its relevance for modulating precipitatio

White-light symmetrization by the interaction of multifilamenting beams

We show experimentally that the interaction of two multifilamenting beams in fused silica with incidence angles up to a few degrees results in an increase in the symmetry of the continuum emission from D2 to C∞ around the axis of symmetry between the two beams. We observe an intense white disk between the locations of the individual conical emission patterns, reducing the conical emission in each of them. We attribute this behavior to an enhanced self-phase modulation in the interference region between the two beams. This frequency conversion depletes by more than 40% the energy initially available in the photon bath to feed filaments