Benjamin Forestier

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.

Laser-induced periodic annular surface structures on fused silica surface

We report on the formation of laser-induced periodic annular surface structures on fused silica irradiated with multiple femtosecond laser pulses. This surface morphology emerges after the disappearance of the conventional laser induced periodic surface structures, under successive laser pulse irradiation. It is independent of the laser polarization and universally observed for different focusing geometries. We interpret its formation in terms of the interference between the reflected laser field on the surface of the damage crater and the incident laser pulse.

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.

Tesla coil discharges guided by femtosecond laser filaments in air

A Tesla coil generator was designed to produce high voltage pulses oscillating at 100 kHz synchronisable with a nanosecond temporal jitter. Using this compact high voltage generator, we demonstrate reproducible meter long discharges in air at a repetition rate of 1 Hz. Triggering and guiding of the discharges are performed in air by femtosecond laser filaments.

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.

Laser beam self-symmetrization in air in the multifilamentation regime

We show experimental and numerical evidence of spontaneous self-symmetrization of focused laser beams experiencing multi-filamentation in air. The symmetrization effect is observed as the multiple filaments generated prior to focus approach the focal volume. This phenomenon is attributed to the nonlinear interactions amongst the different parts of the beam mediated by the optical Kerr effect, which leads to a symmetric redistribution of the wave vectors even when the beam consists of a bundle of many filaments.

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.

Ciliary white light generated during femtosecond laser ablation on transparent dielectrics

Intense laser pulses impinged on the surface of solid dielectrics lead to ablation, massive material removal from the surface. With femtosecond laser pulses, many interesting phenomena have been observed during this process, such as surface periodic fringe with period much less than the laser wavelength (0.1λ~0.5λ), formation of arrays of nanometer-scale rods, etc. So far, little attention has been given to the evolution of the laser pulse itself during the ablation process. Here we present the first experimental investigation on the spatial and spectral evolution of femtosecond laser pulse during laser ablation of transparent materials. A universal new phenomenon, coined as ciliary white-light was observed, which also provides a real time in-situ observation of laser ablation on transparent materials.