Magali Durand

Kilometer range filamentation

We demonstrate for the first time the possibility to generate long plasma channels up to a distance of 1 km, using the terawatt femtosecond T&T laser facility. The plasma density was optimized by adjusting the chirp, the focusing and beam diameter. The interaction of filaments with transparent and opaque targets was studied.

Triggering, guiding and deviation of long air spark discharges with femtosecond laser filament

We show for the first time that filaments are able to divert electric discharges from their normal path. Comparison between negative and positive discharge polarities reveals important differences in the guiding mechanism.

Maker fringes in the Terahertz radiation produced by a 2-color laser field in air

The terahertz radiation produced by a 2-color femtosecond laser scheme strongly saturates and develops an oscillatory behavior with increasing power of the driving femtosecond laser pulses. This is explained by the formation of a plasma channel due to filamentation. Due to dispersion inside the filament and the Gouy phase shift, the phase difference between the 800 nm and 400 nm pulses varies along this plasma emitter. As a result, the local THz radiations generated along the filament interfere destructively or constructively, which manifests itself in the form of Maker fringes.

Radiofrequency conical emission from femtosecond filaments in air

We show that the broadband conical emission associated with filaments in air extends down to the radiofrequency region. This rf emission which originates from the longitudinal oscillation of charged ions formed during filamentation is strongly enhanced by the presence of a longitudinal static electric field.

Experimental observation of a traveling plasma grating formed by two crossing filaments in gases

The spatial motion and effective duration of a traveling plasma grating formed by two interfering femtosecond laser filaments in gases is characterized by its Doppler effect imparted on a probe pulse. The shift velocity determined experimentally agrees with the theoretical calculations.

Third Harmonic Generation from Perturbed Femtosecond Filaments in Air

We investigate third harmonic generation from femtosecond laser filaments. A two-order-of-magnitude enhancement of third harmonic light is observed when the (signal) filament is perturbed by a second laser (pump) filament. This enhancement is studied as function of laser polarization, time delay between the pump and signal filaments, the pump filament energy, etc. Based on these systematic results, we attribute the enhancement to a quenching of the interference effects of the third harmonic generated in the first and second half of the signal filament. Numerical simulations based on a two-color propagation model reproduce well the experimental observations and confirms our explanation.

Damage effects of filaments on non-transparent materials at long distances

We observed multiple filamentation of a Terawatt fs-laser beam (λ = 800 nm, E = 170 mJ/pulse) after 1 km horizontal propagation in the atmosphere. The interaction of these filaments with the non-transparent targets was studied. The filaments were strong enough to damage the surface of optical windows like Ge and ZnSe even at long distances and under turbulent conditions. The damage effects were analysed by studying the modulation transfer function (MTF), the spectral transmission loss, the ablation depth and the damage threshold. LIBS was applied to estimate the plasma temperature during the interaction process.

Coherent control of an electric dipole in air plasma created by femtosecond laser pulses

Air plasma excited by a 800 nm femtosecond pulse with its second harmonic is capable of emitting intense Terahertz (THz) radiation, which is of great interest due to its unique potential for stand-off THz applications [1, 2]. In this paper, we report the experimental observation of an electric dipole moment in such a plasma and its coherent control.