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SUMMARY:Analyzing and Controlling the Atmosphere with High Intensity Laser
 s
DTSTART:20160205T141500
DTSTAMP:20260609T230352Z
UID:6d844e4f4b74a62bc9bfcda84ca8ed86dfa8a0c9619d59aaa92fe32e
CATEGORIES:Conferences - Seminars
DESCRIPTION:Jean-Pierre WolfGroup of Applied Physics\, University of Genev
 a\nFilamentation of multi TW-class lasers opened new perspectives in atmos
 pheric research [1]. Laser filaments are self-sustained light structures o
 f typically 100 um diameter and up to hundreds of meters in length\, widel
 y extending the traditional linear diffraction limit. They stem from the d
 ynamic balance between Kerr self-focusing and defocusing by the self-gener
 ated plasma and/or negative higher-order Kerr terms [2]. New paradigms rec
 ently emerged from the self-organization of these laser filaments\, associ
 ated to e.g.\, oceanic rogue wave dynamics or phase transition phenomena l
 ike percolation [3].\nWhile propagating non-linearly in air\, the ultra-in
 tense laser filaments generate a coherent supercontinuum (from 230 nm to 4
  um) by self-phase modulation (SPM). This "white light laser" is an ideal 
 source for Lidar (Light Detection and Ranging) measurements\, as it covers
  the absorption bands of most atmospheric pollutants. Field applications\,
  such as multi-pollutant analysis\, remote detection and identification of
  bioaerosols (bacteria)\, and remote filament induced breakdown spectrosco
 py will be presented. Moreover\, coherent control approaches using shaped 
 femtosecond laser pulses showed unprecedented capabilities for discriminat
 ing molecules exhibiting almost identical linear spectra such as PAHs and 
 proteins. Recently\, we showed that the time-reversibility of filamentatio
 n allows to explicitly design the laser pulse shape so that propagation se
 rves as a non-linear field synthesizer at a remote target location in orde
 r to enforce coherent control strategies at a distance.\nLaser filaments r
 ecently gave rise to other spectacular atmospheric applications: The contr
 ol of lightning strikes and of water condensation. Using the Teramobile la
 ser system\, we first demonstrated the capability of filaments to trigger 
 Megavolt discharges in the laboratory. Real scale experiments were then ca
 rried out\, at the Langmuir Laboratory in New Mexico. Discharges triggered
  by the laser within thunderclouds could be clearly identified [4]. Althou
 gh no lightning strike could be guided towards the Earth\, these results p
 rovide a significant step towards laser based lightning control.\nBased on
  field experiments in various atmospheric conditions\, we showed that lase
 r filaments can induce water condensation and fast droplet growth up to se
 veral µm in diameter in the atmosphere [5] as soon as the relative humidi
 ty (RH) exceeds 70%. This effect mainly relies on photochemical mechanisms
  allowing efficient binary H2O–HNO3 condensation [6]. Thermodynamic as w
 ell as kinetic numerical modelling based on this scenario semi-quantitativ
 ely reproduces the experimental results\, supporting this interpretation. 
 Finally\, using the AIDA cloud chamber in Karlsruhe\, we investigated the 
 possible modulation of the cirrus clouds albedo by manipulating the size d
 istribution of these ice crystals using high intensity lasers\, and discov
 ered that radiative forcing properties of these clouds can potentially be 
 inverted by high intensity laser’s radiation [7].\nReferences:\n[1] J. K
 asparian et al\, Science 301\, 61-64 (2003)\n[2] P. Bejot et al\, Phys.Rev
 .Lett. 104\, 103903 (2011)\n[3] W. Ettoumi et al\,  Phys.Rev.Lett. 114\, 
 063903 (2015)\n[4] J. Kasparian et al\, Opt. Express 16\,  5757-5763 (200
 8)\n[5] P. Rohwetter et al\, Nature Photonics 4\, 451 - 456 (2010)\n[6] S.
 Henin et al\, Nature Communications. 2\, 456 (2011)\n[7] T. Leisner et al\
 , PNAS 110\, 10106-10110 (2013)
LOCATION:PH-L1 503 
STATUS:CONFIRMED
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