Bernard Prade

CONICAL EMISSION FROM SELF-GUIDED FEMTOSECOND PULSES IN AIR

Conical emission in the forward direction is observed from intense femtosecond light pulses propagating through air over long distances. The conical emission is attributed to Cerenkov radiation from a dynamic self-guiding structure consisting of a weakly ionized core surrounded by Kerr cladding.

Writing of permanent birefringent microlayers in bulk fused silica with femtosecond laser pulses

Permanent birefringent structures with controllable microscopic dimensions are inscribed in pure fused silica platelets. The birefringence properties of transmission gratings and of a quasi-uniform layer have been established.

Infrared extension of the supercontinuum generated by femtosecond terawatt laser pulses propagating in the atmosphere

We investigated the spectral behavior of a white-light continuum generated in air by 2-TW femtosecond laser pulses at 800 nm. The spectrum extends at least from 300 nm to 4.5 mum. From 1 to 1.6 mum the continuums intensity increases strongly with the laser energy and depends on the initial chirp.

Time-evolution of the plasma channel at the trail of a self-guided IR femtosecond laser pulse in air

The density and decay kinetics of a plasma channel created in air by a self-guided intense ultra-short laser pulse is determined by a new electric cross-conductivity method and by diffraction interferometry. A fast decay is measured, due to the dominant intrinsic recombination process at high plasma density.

Study of damage in fused silica induced by ultra-short IR laser pulses

We report on a new type of permanent damage obtained in bulk fused silica by focusing IR femtosecond laser pulses with microjoule energy. It consists of an uniaxial birefringence zone over a lateral size of a few microns and a depth of a few tens of microns. The birefringence zone is followed by sub-micrometer filamentary cracks extending up to 80 μm. Nonlinear pulse propagation plays a crucial role in the onset of this type of damage.

Coherent subterahertz radiation from femtosecond infrared filaments in air

We report on what is believed to be the first observation of coherent subterahertz (sub-THz) emission from a 1-m string in the atmosphere. The sub-THz pulse emitted by the filamentary structure from an intense IR femtosecond laser pulse is detected perpendicularly to the laser propagation axis by use of two heterodyne detectors at 94+/-1 and 118+/-1GHz . We describe the characteristics of this emission and show evidence of constructive interference between two separate strings.

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.

Forward THz radiation emission by femtosecond filamentation in gases: theory and experiment

A transition-Cherenkov electromagnetic emission by a femtosecond laser pulse propagating in a self-induced plasma channel in air has been very recently proposed as mechanism for production of terahertz (THz) radiation in the forward direction. In this paper, we study in detail the theory of the transition-Cherenkov process. The theoretical model is developed and compared with recent experimental results for several gases.

Anomalous long-range propagation of femtosecond laser pulses through air: moving focus or pulse self-guiding?

Self-guided propagation of femtosecond laser pulses is studied for a converging-beam configuration. Channeling of the pulse energy through various gases is observed over distances well beyond the lens focal point, a fact that cannot be explained by the moving-focus model. The results are in good agreement with three-dimensional numerical simulations.

Determination of the time dependence of n2 in air

Abstract Using cross-phase modulation, the dynamics of the Kerr-like response of air is studied. Spontaneous resurgences of the induced non-linear polarisation are observed, in good agreement with a theoretical model.