Formation of filament and plasma channel by the Bessel incident beam in Ar gas: role of the outer part of the beam

Abstract

We theoretically investigate the formation of filament and plasma channel in Ar gas by intense femtosecond pulses in the Bessel, truncated Bessel, and combination of two Gaussian modes. Through the numerical results obtained by solving the generalized nonlinear Schrödinger equation coupled with the electron density evolution equation, we find that there is a radial energy flow during the propagation, which implies that the outer part of the Bessel beam serves as an energy reservoir for the filament formed around the central peak. The results we obtain for the Bessel and truncated Bessel incident beams are consistent in that we can obtain a longer filament and plasma channel if more energy is reserved in the outer part of the Bessel incident beam. More interestingly we show that the combined use of two Gaussian beams with different beam diameters increases the energy stored in the outer part of the beam, and as a result the lengths of the filament and plasma channel become remarkably longer. This can be a practical choice to improve the propagation properties.