Formation of a conducting channel in air by self-guided femtosecond laser pulses

We report a drastic reduction of air resistivity following the passage of a self-guided femtosecond pulse from a Ti:sapphire laser system at 800 nm wi th energies per pulse between 1 and 14 mJ and a pulse duration of 120 fs. C onnected plasma filaments with a length that can exceed 150 cm are created by these pulses. The presence of a conducting plasma channel results from m ultiphoton ionization of air molecules in the filament core. [S1063-651X(99 )51210-5].