Some Properties of Femtosecond Laser Filamentation Relevant to Atmospheric Applications Part I. The Robustness of Filamentation.

When ultrashort (fs), high-power laser pulses propagate through the atmosphere, extended plasma filaments form and emit white light in a spectral range spanning from the ultraviolet (230 nm) to the infrared (4.5 µm). This strongly non-linear optical phenomenon results from a dynamical balance between respectively focusing and defocusing Kerr- and plasma-lenses, which are formed by a nonuniform, intensity-dependent refractive index across the laser beam profile. This non-linear propagation regime opens the way to various applications in atmospheric sciences, such as white-light Lidar relying on the white light continuum, which can be observed up to high altitudes and allows multicomponent remote sensing. Other applications rely on the ability of the filaments to deliver high-intensities and induce non-linear optical effects at remote locations, e.g. bioaerosols remote sensing or solid target analysis. Furthermore, the ionization of the fs-laser-induced filaments permits to control high-voltage discharges, opening the way to laser lightning rods. This chapter shall review the basic properties of filamentation, with a particular emphasis on one spectacular feature: Their ability to propagate unperturbed across clouds and fogs. [ABSTRACT FROM AUTHOR]