Electrical conductivity of long plasma channels in air generated by self-guided femtosecond laser pulses

By slightly focussing similar to 1 TW femtosecond laser pulses, we generated long self-stabilizing filaments in air. Free carriers generated by the pulse move in the electrical field of a bias voltage along these filaments. This is a direct measurement demonstrating the creation of a plasma (n(e) > 10(12) cm(-3)) in the filaments, which plays a crucial role in the interplay of diffraction and self-focussing, leading to the formation of long stable channels. These filaments may have applications for laser-triggered lightning.