Simultaneous length extension and temporal prolongation of high-density plasma filaments generated by a femtosecond laser in the air

We experimentally demonstrate a simultaneous spatial extension and temporal prolongation of plasma wire generated by a high-power femtosecond laser undergoing filamentation. A single femtosecond laser pulse, transmitted through a specially designed telescopic lens array, creates three concatenated segments of the plasma wire with total length of over 3 meters and free electron density of ∼10¹⁶ cm⁻³ along the entire distance. The plasma filaments were irradiated by a secondary nanosecond laser that propagates collinear to the plasma wire. The plasma wire absorbs energy from the secondary laser and its lifetime is prolonged from about 3 ns to above 30 ns. The obtained plasma wire length and lifetime prolongation is limited only by the fs/ns lasers parameters.