Field measurements suggest the mechanism of laser-assisted water condensation

Abstract

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.

Higher-order Kerr effects improve quantitative modelling of harmonics generation and laser filamentation

“…This finding confirms that our understanding of laser filamentation has to be updated, which will in particular impact the determination of the optimal conditions for the potential applications [2,15] of laser filamentation, like cloudmaking [16] and lightning control [17].…”

Cooperative effect of ultraviolet and near-infrared beams in laser-induced condensation

“…This mechanism was confirmed by the correlation between NO x , O 3 , and nanoparticle production, 19 the detection of NO 3 À ions in laser-generated particles, 12 as well as pH values down to 2 in laser-generated snowflakes in a diffusion cloud chamber. 14 Oxidized volatile organic compounds (VOCs), which are known to significantly enhance water vapor condensation in the atmosphere, 20 were more recently shown to offer an alternative pathway in the laser-induced condensation process.…”

“…[6][7][8] Filamentation is due to the competing effects of Kerr self-focusing, plasma defocusing, and the negative higher order Kerr terms 9 at high intensities (>10 13 -10 14 W/cm 2 ). 10 The resulting plasma wake modifies the physico-chemical properties of the air, allowing the formation of liquid [11][12][13] or solid 14,15 aerosol particles in sub-saturated air, in both the atmosphere 12 and the laboratory. 16 This phenomenon is promising as a technique for analyzing and possibly modifying both microscopic and macroscopic cloud behaviors, 15 in particular, if the type, number, and size distribution of droplets can be controlled.…”

Multijoule scaling of laser-induced condensation in air

“…10,11 They convey a typical intensity of 5 Â 10 13 W/cm 2 at kilometerrange distances, 12 generating large amounts of oxidized species like O 3 , NO, and NO 2 , which subsequently generate hygroscopic HNO 3 . 13 The latter allows binary HNO 3 -H 2 O condensation well below 100% relative humidity (RH), 14 in a similar manner to the well-known H 2 SO 4 -H 2 O binary condensation. [15][16][17][18] However, work up to now was restricted to moderate laser energies (some hundreds of mJ or less) and powers (a few TW), which are unable to initiate macroscopic effects on large atmospheric volumes.…”