Riad Bourayou

White-light filaments for multiparameter analysis of cloud microphysics

We present a lidar technique using femtosecond-terawatt laser pulses to perform a multiparameter analysis of cloud microphysics. Particle size and density within the cloud are deduced from the multispectral multiple scattering pattern of an ultrashort laser pulse. Furthermore, the spectral analysis of the atmospheric transmission of the white-light continuum from the same laser source yields temperature and relative humidity.

Femtosecond LIDAR: new perspectives of atmospheric remote sensing

High-power femtosecond laser pulses can lead to strong nonlinear interactions during the propagation through a medium. In air the well known self-guiding effect produces long intense and moderately ionized filaments, in which a broad white-light continuum from the near UV to the mid IR is generated. The forward directed white-light can be used to do range resolved broadband absorption measurements, which opens the way to a real multi-component lidar for the simultaneous detection of several trace gases. On the other hand, enhanced nonlinear scattering and characteristic emission from the filament region, as well as from the interaction of intense pulses with aerosols, can be observed. This opens perspectives towards a novel kind of analysis of atmospheric constituents, based upon nonlinear optics. Additionally, the conductivity of the filaments can be used for lightning control. Here we present the basic concepts of the femtosecond lidar, laboratory experiments and recent results of atmospheric measurements.

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.

Vertical propagation of ultrashort laser pulses in the atmosphere and lidar measurements using the Teramobile

Using Teramobile laser, a mobile integrated system providing 5 TW peak power in 100 fs pulses, near to a 2 m astronomical telescope, we could for the first time image the femtosecond beam from the side up to altitudes of 25 km. Spectroscopic measurements of the lidar return were performed, in the infrared as well as in the visible.