FilAtmo · Laser Filamentation for Probing and Controlling Atmospheric Processes

The prevention of damaging weather phenomena like floods, hail and lightning strikes has been a dream for centuries. We propose a highly innovative approach relying on laser filaments for both triggering and guiding lightning and produce water condensation in the atmosphere. Filaments are self-sustained light strings of typ. 100 um diameter and hundreds of meters length in air, bear very high intensities and are electrically conductive through molecular ionization.The filamentation process in air was considered until recently as resulting from the dynamic balance between the optical Kerr effect and defocusing by the self-generated plasma. Our unexpected discovery, last year, that filaments are governed by negative higher-order Kerr effect (HOKE), opened both basic physical questions about the stabilization mechanism and new opportunities to optimize the envisioned applications to lightning triggering and cloud condensation.We propose first to study in the laboratory the physical origin of the alternated signs of HOKE in gases, which are suspected to stem from populated bound states. Coherently controlling these bound states in rare gases and air will allow us to tailor the HOKE inversion, and consequently to control the filament process itself. Optimal pulse shapes will then be sought by adaptive (closed loop) techniques to maximize the plasma density and lifetime in filaments for lightning control applications. Similar coherent control approaches will be performed for optimizing the complex photochemistry that leads to water vapor condensation in the atmosphere.We will then apply the optimal pulse shapes to real scale field experiments. To this end we intend to use the mobile TW laser from the Teramobile consortium, which we are part of, in order to perform two extensive campaigns for real-scale lightning control (in Lugano) and haze/cloud generation (in Geneva). These experiments will constitute the first coherent manipulation of atmospheric process.