Vol. 20, issue 01, article # 7

Abstract:

We have studied, using a numerical method, transformation of the spectral, energy, and angular characteristics of the supercontinuum formed by a femtosecond-duration pulsed laser radiation in air. It has been shown that transformation of the frequency spectrum of an ultrashort pulse after its self-focusing and the fraction of its energy transformed into the energy of supercontinuum are mainly determined by the length of a light filament. It has been established that the angular size of a femtosecond-duration pulsed laser radiation beam sharply increases after passing through the region of a global nonlinear focus and then it gradually grows in the zone of beam filamentation approaching some limiting value. The increase of the initial power of radiation yields an increase of the limiting angular divergence of the beam. The angular size of the spectral components of supercontinuum in its IR and visible wings is larger than the beam divergence averaged over the entire spectrum. The excess divergence is larger in the IR wing and can reach two times over the average one.