Behavior of multiply filamentation in femtosecond impulse

This paper is devoted to the investigation of the femtosecond pulse propagation in the air by means of numerical methods. The phenomenon behavior is determined by the relation between the multiphoton ionization and small-scale self-focusing (filamentation). The step-by-step behavior of this process was established, where the evolution of filamentation takes place without energy losses till the intensity reaches the threshold value. Then the dissipation for ionization comes into play and the intensity starts to decrease under defocusing influence of electron plasma. The conditions for repeated self-focusing can be formed after the intensity is below the ionization threshold. Typical features of the filamentation final stage can be explained by means of the Bespalov-Talanov theory.