A simple method to significantly increase filaments’ length and ionization density
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- Daigle, J., Kosareva, O., Panov, N. et al. Appl. Phys. B (2009) 94: 249. doi:10.1007/s00340-008-3270-5
A simple method to produce longer filaments with higher ionization density in air by controlling the diameter of an aperture in the laser beam path is studied via an analysis of the backscattered N2 fluorescence collected by LIDAR. Significant increase in the fluorescence signal (approximately by a factor of five depending on the conditions) and an increased filament length was observed at an optimum diameter. 3D + time stochastic numerical simulations have 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. The optimum range of aperture sizes is the same for the initial transverse perturbation scale variation at least within a factor of three.