17 research outputs found
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
1-J white-light continuum from 100-TW laser pulses
We experimentally measured the supercontinuum generation using 3-J, 30-fs laser pulses and measured white-light generation at the level of 1 J. Such high energy is allowed by a strong contribution to the continuum by the photon bath, as compared to the self-guided filaments. This contribution due to the recently observed congestion of the filament number density in the beam profile at very high intensity also results in a wider broadening for positively chirped pulses rather than for negatively chirped ones, similar to broadening in hollow-core fibers