Background reservoir:: its crucial role for long-distance propagation of femtosecond laser pulses in air

We report an experiment to demonstrate the crucial effect of the so-called background reservoir during the propagation of femtosecond laser pulses in air. The background reservoir was blocked by allowing only the filament to pass through a pinhole generated by the filament itself in an aluminum foil. We observed that the filamentation process is terminated immediately after the pinhole. Consequently, to achieve long-range filamentation, it is necessary to maintain the dynamic energy exchange between the reservoir and the self-foci.