Colloquium: Jean-Pierre Wolf

    Date: 
    Thursday, March 10, 2016 - 3:30pm - 5:00pm
    Location: 
    Meinel 307
    Description: 

    Analysing and Controlling the Atmospherewith High Intensity Lasers

    Abstract(s): 

    Filamentation of multi TW-class lasers opened new perspectives in atmospheric research1. Laser filaments are self-sustained light structures of typically 100 um diameter and up to hundreds of meters in length, widely extending the traditional linear diffraction limit. They stem from the dynamic balance between Kerr self-focusing and defocusing by the self-generated plasma and/or negative higher-order Kerr terms2. New paradigms recently emerged from the self-organization of these laser filaments, associated to e.g., oceanic rogue wave dynamics or phase transition phenomena like percolation3.

    While propagating non-linearly in air, ultra-intense 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 spectroscopy will be presented. Moreover, coherent control approaches using shaped femtosecond laser pulses showed unprecedented capabilities for discriminating molecules exhibiting almost identical linear spectra such as PAHs and proteins. Recently, we showed that the time-reversibility of filamentation allows to explicitly design the laser pulse shape so that propagation serves as a non-linear field synthesizer at a remote target location in order to enforce coherent control strategies at a distance.

    Laser filaments recently gave rise to other spectacular atmospheric applications: The control of lightning strikes and of water condensation. Using the Teramobile laser system, we first demonstrated the capability of filaments to trigger Megavolt discharges in the laboratory. Real scale experiments were then carried out, at the Langmuir Laboratory in New Mexico. Discharges triggered by the laser within thunderclouds could be clearly identified4. Although no lightning strike could be guided towards the Earth, these results provide a significant step towards laser based lightning control. 

    Based on field experiments in various atmospheric conditions, we showed that laser filaments can induce water condensation and fast droplet growth up to several µm in diameter in the atmosphere5 as soon as the relative humidity (RH) exceeds 70%. This effect mainly relies on photochemical mechanisms allowing efficient binary H2O–HNO3 condensation6. Thermodynamic as well as kinetic numerical modelling based on this scenario semi-quantitatively 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 distribution of these ice crystals using high intensity lasers, and discovered that radiative forcing properties of these clouds can potentially be inverted by high intensity laser’s radiation7.

    1J. Kasparian et al, Science 301, 61-64 (2003)

    2P. Bejot et al, Phys.Rev.Lett. 104, 103903 (2011)

    3W. Ettoumi et al,  Phys.Rev.Lett.114, 063903 (2015)

    4J. Kasparian et al, Opt. Express 16,  5757-5763 (2008)

    5P. Rohwetter et al, Nature Photonics 4, 451 - 456 (2010)

    6S.Henin et al, Nature Communications. 2, 456 (2011)

    7T. Leisner et al, PNAS110, 10106-10110 (2013)

    Speaker Bio(s): 

    After having lead research projects at the ETH-Lausanne and the University Berlin and being a Professor at the University Lyon and visiting Professor at Yale University, Prof. J.P. Wolf joined the University of Geneva in 2005. Since then he set up a new team at the Group of Applied Physics (GAP), dedicated to the biomedical and atmospheric  applications of ultrashort lasers (www.gap.unige.ch/biophotonics). His current activities concentrate on advanced non-linear microscopy and imaging of living cells and applications of laser filamentation to atmospheric monitoring. He was awarded an ERC Proof of Concept Grant  in 2013, an ERC Advanced Grant in 2011, the Prix La Recherche in 2005, the Grand Prix de Physique de l’Academie des Sciences (France) in 2002, and the Technology Award of the Land Berlin-Brandenburg in 1993. He is member of the Institut Universitaire de France since 1996 and NATO Senior Fellow.