Uniform lifetime prolongation of a high density plasma channel left in the wake of femtosecond filament

We demonstrate uniform lifetime prolongation of an entire plasma filament generated by a high-power femtosecond laser pulse. The entire filament is irradiated by a secondary nano-second laser pulse that co-propagates with the femtosecond laser. The plasma filament partially absorbs the nanosecond laser radiation, and plasma lifetime is extended along the entire channel resulting in a smooth and continuous high-density plasma column with lifetime longer than 30 ns. We present an experimental and theoretical study of the intensity range of the secondary laser required for effective lifetime prolongation and the behavior of the plasma density at the onset of breakdown triggered by the secondary laser. Our study shows that an efficient prolongation of the lifetime of plasma filament occurs in the intensity range of 0.03-0.3 TW/cm².