Ultrafast laser filamentation control techniques for remote applications

Two methods of filamentation control for remote applications were studied. The first one consisted in an adaptive optic system, implemented in a specially designed focusing beam expander, which corrected for wavefront aberrations. Using this setup we are able to generate extraordinarily strong nitrogen signals at a distance as far as 90 m using 40 mJ laser pulses. Moreover, the filaments produced were used in a remote sensing scheme to detect and identify multiple targets such as trace hydrocarbon gases, solid metallic targets and aqueous aerosol clouds. The other method consists in a filament regularization method where a circular aperture of variable diameter is centered on the laser propagation axis, prior to filamentation. Longer filaments with higher ionization densities were produced in air and studied via the backscattered N
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fluorescence. 3D + time stochastic numerical simulations has shown that the optimum aperture size corresponds to the case of multiple filament ‘squeezing’ around the propagation axis forming the regularized elongated structure with higher overall amount of plasma.