a step towards modulating precipitation?

We review the recent results about laser-induced condensation based on self- guided filaments generated by ultrashort laser pulses. After recalling the physico-chemistry of cloud particle formation in the atmosphere and the physics of laser filamentation, we discuss experimental results on laser- induced condensation and its relevance for modulating precipitation

PCF-Based Cavity Enhanced Spectroscopic Sensors for Simultaneous Multicomponent Trace Gas Analysis

A multiwavelength, multicomponent CRDS gas sensor operating on the basis of a compact photonic crystal fibre supercontinuum light source has been constructed. It features a simple design encompassing one radiation source, one cavity and one detection unit (a spectrograph with a fitted ICCD camera) that are common for all wavelengths. Multicomponent detection capability of the device is demonstrated by simultaneous measurements of the absorption spectra of molecular oxygen (spin-forbidden b-X branch) and water vapor (polyads 4v, 4v + δ) in ambient atmospheric air. Issues related to multimodal cavity excitation, as well as to obtaining the best signal-to-noise ratio are discussed together with methods for their practical resolution based on operating the cavity in a “quasi continuum” mode and setting long camera gate widths, respectively. A comprehensive review of multiwavelength CRDS techniques is also given

Untersuchungen zur durch Femtosekunden Laser-Filamente induzierten atmosphärischen Kondensation

The aim of the present work is to gain an understanding of femtosecond laser- induced atmospheric condensation of particles, and to investigate its potential applicability for laser remote sensing of the atmosphere. The primary focus is on terawatt laser pulses undergoing multiple filamentation, and on naturally occuring atmospheric conditions. The investigations are motivated by previous observations, showing the ability of high intensity femtosecond laser radiation to cause the condensation of fog droplets out of the gas phase, under conditions of high water vapour supersaturation. In the present work similar is shown to hold for multiply filamenting terawatt laser pulses. Furthermore, their ability to cause condensation of particles is observed to remain, to some extent, even under atmospheric conditions of water vapour subsaturation. An initial attempt to use filament-induced condensation as a tool for atmospheric remote sensing shows its basic feasibility, but it also exposes the technical and fundamental challenges that remain to be overcome. Using auxiliary results from laboratory experiments conducted by project partners a model for filament-induced condensation is developed, which makes predictions reasonably well in accord with experimental observations.Die vorliegende Arbeit hat zum Ziel, die durch intensive Femtosekunden- Laserpulse induzierten Kondensation von Partikeln aus der Gasphase zu verstehen, und deren Anwendbarkeit im Rahmen der lasergestützten Atmosphärenfernerkundung zu erproben. Dabei liegt das primäre Interesse auf Laserpulsen im Leistungsbereich von Terawatt, die während der Ausbreitung mehrfach filamentieren und auf natürlich in der unteren Atmosphäre auftretenden Bedingungen. Die Untersuchungen sind motiviert durch bekannte frühere Beobachtungen, durch die die grundsätzliche Fähighkeit hochintensiver Femtosekunden-Laserstrahlung nachgewiesen werden konnte, unter mit Wasserdampf übersättigten Bedingungen die Kondensation von Nebeltröpfchen aus der Gasphase herbeizuführen. Entsprechendes kann im Rahmen dieser Arbeit auch für den Fall der mehrfach filamentierenden Terawatt-Laserpulse gezeigt werden. Darüberhinaus wird beobachtet, dass diese Fähigkeit in gewissem Rahmen auch in Wasserdampf-untersättigter Atmosphäre erhalten bleibt. Ein erster Versuch, Filament-induzierte Kondensation für die laserbasierte Atmosphärenfernerkundung nutzbar zu machen, zeigt die prinzipielle Machbarkeit, aber auch, welche technischen und fundamentalen Probleme noch zu lösen bleiben. Unter Zuhilfenahme zusätzlicher Ergebnisse aus Labormessungen von Projektpartnern wird ein Modell für die Filament-induzierte atmosphärische Kondensation entwickelt, dessen Vorhersagen mit den experimentellen Resultaten in Einklang sind

Long-distance remote laser-induced breakdown spectroscopy using filamentation in air

International audienceWe demonstrate remote elemental analysis at distances up to 90 m, using a laser-induced breakdown spectroscopy scheme based on filamentation induced by the nonlinear propagation of unfocused ultrashort laser pulses. A detailed signal analysis suggests that this technique, remote filament-induced breakdown spectroscopy, can be extended up to the kilometer range

Improved laser triggering and guiding of meqavolt discharges with dual fs-ns pulses

International audienceWe demonstrate that the capacity of ultrashort high-power laser pulses to trigger and guide high-voltage discharges can be significantly enhanced by a subsequent visible nanosecond laser pulse. The femtosecond pulse induces a bundle of filaments, which creates a conducting channel of low density and cold plasma connecting the electrodes. The subsequent laser pulse photodetaches electrons from O2- ions in the electrode leader. The resulting electrons allow efficient heating by Joule effect in a retroaction loop, resulting in a 5% reduction of the breakdown voltage

Optimal control of filamentation in air

The authors demonstrate optimal control of the propagation of ultrashort, ultraintense (multiterawatt) laser pulses in air over distances up to 36m in a closed-loop scheme. They optimized three spectral ranges within the white-light continuum as well as the ionization efficiency. Optimization results in signal enhancements by typical factors of 2 and 1.4 for the target parameters. The optimization results in shorter pulses by reducing their chirp in the case of white-light continuum generation, while they correct the pulse from its defects and set the filamentation onset near the detector as far as air ionization is concerned

Electric events synchronized with laser filaments in thunderclouds

We investigated the possibility to trigger real-scale lightning using ionized filaments generated by ultrashort laser pulses in the atmosphere. Under conditions of high electric field during two thunderstorms, we observed a statistically significant number of electric events synchronized with the laser pulses, at the location of the filaments. This observation suggests that corona discharges may have been triggered by filaments

Laser-induced plasma cloud interaction and ice multiplication under cirrus cloud conditions

Potential impacts of lightning-induced plasma on cloud ice formation and precipitation have been a subject of debate for decades. Here, we report on the interaction of laser-generated plasma channels with water and ice clouds observed in a large cloud simulation chamber. Under the conditions of a typical storm cloud, in which ice and supercooled water coexist, no direct influence of the plasma channels on ice formation or precipitation processes could be detected. Under conditions typical for thin cirrus ice clouds, however, the plasma channels induced a surprisingly strong effect of ice multiplication. Within a few minutes, the laser action led to a strong enhancement of the total ice particle number density in the chamber by up to a factor of 100, even though only a 10−9 fraction of the chamber volume was exposed to the plasma channels. The newly formed ice particles quickly reduced the water vapor pressure to ice saturation, thereby increasing the cloud optical thickness by up to three orders of magnitude. A model relying on the complete vaporization of ice particles in the laser filament and the condensation of the resulting water vapor on plasma ions reproduces our experimental findings. This surprising effect might open new perspectives for remote sensing of water vapor and ice in the upper troposphere