Analyzing and Controlling the Atmosphere with High Intensity Lasers
Event details
| Date | 05.02.2016 |
| Hour | 14:15 |
| Speaker |
Jean-Pierre Wolf Group of Applied Physics, University of Geneva |
| Location |
PH-L1 503
|
| Category | Conferences - Seminars |
Filamentation of multi TW-class lasers opened new perspectives in atmospheric research [1]. 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 terms [2]. 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 percolation [3].
While propagating non-linearly in air, the 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 identified [4]. 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 atmosphere [5] as soon as the relative humidity (RH) exceeds 70%. This effect mainly relies on photochemical mechanisms allowing efficient binary H2O–HNO3 condensation [6]. 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 radiation [7].
References:
[1] J. Kasparian et al, Science 301, 61-64 (2003)
[2] P. Bejot et al, Phys.Rev.Lett. 104, 103903 (2011)
[3] W. Ettoumi et al, Phys.Rev.Lett. 114, 063903 (2015)
[4] J. Kasparian et al, Opt. Express 16, 5757-5763 (2008)
[5] P. Rohwetter et al, Nature Photonics 4, 451 - 456 (2010)
[6] S.Henin et al, Nature Communications. 2, 456 (2011)
[7] T. Leisner et al, PNAS 110, 10106-10110 (2013)
While propagating non-linearly in air, the 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 identified [4]. 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 atmosphere [5] as soon as the relative humidity (RH) exceeds 70%. This effect mainly relies on photochemical mechanisms allowing efficient binary H2O–HNO3 condensation [6]. 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 radiation [7].
References:
[1] J. Kasparian et al, Science 301, 61-64 (2003)
[2] P. Bejot et al, Phys.Rev.Lett. 104, 103903 (2011)
[3] W. Ettoumi et al, Phys.Rev.Lett. 114, 063903 (2015)
[4] J. Kasparian et al, Opt. Express 16, 5757-5763 (2008)
[5] P. Rohwetter et al, Nature Photonics 4, 451 - 456 (2010)
[6] S.Henin et al, Nature Communications. 2, 456 (2011)
[7] T. Leisner et al, PNAS 110, 10106-10110 (2013)
Practical information
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- Free
Organizer
- Arnaud Magrez and Raphaël Butté