Abstract

The generation of filaments with ultrashort laser pulses is based on the sustained balance between self-focusing (Kerr effect) and ionization. When the peak power of the laser pulse is close to a critical self-focusing power value (P_cr) a single filament develops. If the beam power exceeds about more than 10 times P_cr, modulation instability can cause several co-propagating filaments formed from a single laser beam spontaneously, thus entering into the multiple filaments (MFs) regime. To avoid the random space–time localization of MFs, the initial beam is modified by methods that include, among others, changes in its ellipticity or wavefront shaping. However, although the generation of controlled off-axis MFs has been extensively studied, less attention has been paid to the generation of sequential on-axis MFs. This is the key point of this work.

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