G. Méchain

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.

Triggering and guiding of megavolt discharges by laser-induced filaments under rain conditions

We demonstrate laser control of high-voltage discharges over a gap of 1.2 m filled with a dense water cloud. Self-guided filaments generated by ultrashort laser pulses are transmitted through the cloud and ionize a continuous plasma channel. The cloud typically reduces the discharge probability in given experimental conditions by 30%, but has almost no influence on the threshold required to trigger single discharge events, both in electrical field and laser energy. This result is favorable for real-scale lightning control applications.

A virtual antenna produced in air by intense femtosecond laser pulses

When propagating in air intense femtosecond laser pulses organize into intense self-guided light pulses. In turn, such self-guided pulses generate in their wake extended thin plasma columns. We show that these plasma columns act like antennas able to radiate electromagnetic pulses.

Femtosecond filamentation in air at low pressures

We investigate the influence of air pressure on femtosecond filamentation in the laboratory, in the pressure range between 0.2 and 1 bar. Numerical simulations reproduce the main features of the experimental results.

THz emission from electrically charged femtosecond filaments in air

We observe a strong increase of the THz emission from femtosecond filaments in air in the presence of an applied electric field.

Propagation of TW laser pulses in air and applications to lightning control

In this paper, ultrashort laser pulses while propagating in air undergo filamentation which results from a dynamic balance between Kerr lens focusing and defocusing on laser-induced micro plasma. Such equilibrium leads to a self-guided ionized channel, or filament, with a diameter on the order of 100 /spl mu/m, extending over long distances up to several hundreds of meters. Using the Teramobile laser system providing 250 mJ pulses of 100 fs duration, centered at 800 nm, we have shown that the beam propagation for multi-TW pulses is driven by the interplay between random nucleation of small-scale cells and relaxation to long waveguides. We compare experimental results with simulations. Also, a white-light supercontinuum is generated by self-phase modulation, and mixing with the generated third harmonic generation (THG) extends the spectrum down to 230 nm in the infrared, providing a promising light source for multiparameter remote sensing by Lidar.

Filamentation in air with twin femtosecond laser pulses

We study filamentation in air using a sequence of two intense IR femtosecond laser pulses with variable delay. Increased filament length and pulse shortening is observed, in agreement with simulations.

Femtosecond infrared filaments in air: a source of coherent THz radiation

We observe coherent THz emission from a 1-m plasma string produced by an IR fs laser pulse in atmosphere. The THz pulse is detected perpendicular to the laser propagation axis using heterodyne detection.

How to connect femtosecond laser filaments in air

For the first time we connect two filaments created in air by two femtosecond laser pulses. For a specific time ordering of the pulses a twofold increase of the total filament length is achieved. The direct benefits include improved air plasma conductivity and stronger continuum generation.