عنوان مقاله [English]
نویسندگان [English]چکیده [English]
In this paper, TEA CO2 laser pulses, focused by plasma shutters, by 2.5, 5 and 10 cm focal lengths lenses, have been used in order to generating optical breakdown in different mono up to five atomic molecules. The dependence of the transmitted pulses temporal trace and the sparks geometry on the focusing power as well as the gases pressure, molecular weight and ionization energy were investigated in detail. It has been found that instead of complete removal of the tail part in the transmitted pulses shapes, sometimes a fraction of them is disappeared. For instance, a quenching time gap in 0.05-2.6 µs range is appeared in the transmitted pulses shapes for 2.5 cm focal length. Such a quenching time, of course at lower scales, is also observed for He gas with the other focal lengths. Analyses of the generated plasma plume shapes and the focused laser beams paths have revealed that this behavior is due to quick dropping of the plasma density below the critical level, before the pulse tail is completed.