Experimental study on spatial characteristics of filamentation and propagation of ultrashort pulse laser

The induction effect of air gap discharge induced by ultrashort pulse laser will be affected by the characteristics of laser ionization filamentation. In order to study the spatial characteristics of ultrashort pulse laser ionization filamentation and propagation. Firstly, an experimental platform for studying the spatial characteristics of ultrashort pulse laser ionization filamentation and propagation is established. Then the axial and radial high-resolution optical images of filaments under the conditions of different focal length auxiliary focusing lens are obtained by using the combination of axial and radial detection method. The effectiveness of this observation method is proved by contrasting with the self-focusing and multiple filament correlation theory. By analyzing the relationship between the filament diameter and the laser propagation distance under the condition of 1m and 5m focal length lens assisted focusing, the effects of micro focusing and tight focusing on the filament distance are obtained. The experimental results show that the filament will continue to travel forward for a certain distance with the minimum optical diameter after reaching the minimum optical diameter in the micro focusing mode. So we can obtain a stable plasma channel in this way; In the tight focusing mode, the defocus effect of plasma plays a leading role in the laser propagation process faster. So the filament will disappear rapidly after reaching the minimum optical diameter, which is not conducive to the long-distance filament transmission.