Abstract
We report the influence of femtosecond (fs) laser weakly ionized air channel on characteristics of plasma induced from fs-laser ablation of solid Zr metal target. A novel method to create high temperature, low electron density plasma with intense elemental emission and weak bremsstrahlung emission was demonstrated. Weakly ionized air channel was generated as a result of a non-linear phenomenon. Two-dimensional time-resolved optical-emission images of plasma plumes were taken for plume dynamics analysis. Dynamic physical properties of filament channels were simulated. In particular, we investigated the influence of weakly ionized air channel on the evolution of solid plasma plume. Plasma plume splitting was observed whilst longer weakly ionized air channel formed above the ablation spot. The domination mechanism for splitting is attributed to the long-lived underdense channel created by fs-laser induced weakly ionization of air. The evolutions of atomic/molecular emission intensity, peak broadening, and plasma temperature were analyzed, and the results show that the part of plasma entering weakly ionized air channel features higher initial temperature, lower electron density and faster decay.
Highlights
The propagation of ultrafast laser filaments through transparent media contains complex nonlinear phenomena and results in various exciting potential applications [1,2,3,4]
One single channel formed, which enhanced the interaction between weakly ionized channel and ablated plasma plume because higher laser intensity can be clamped inside the channel, intense influence of weakly ionized air channel on plasma plumes was expected
Femtosecond laser ablated plasma plume can be sucked into the long-lived underdense channel that created by ultrafast laser filamentation phenomenon, and further split into two parts whilst longer weakly ionized air channel formed above the ablation spot
Summary
The propagation of ultrafast laser filaments through transparent media contains complex nonlinear phenomena and results in various exciting potential applications [1,2,3,4]. A filament can be formed when femtosecond (fs) laser power is above the critical power [5], as a result of dynamic balance between self-focusing and defocusing [6]. The laser power density clamped in the filament channels is in the order of 1013 W/cm or even higher [12,13], which is sufficient for material ablation. Fs-laser filament ablation, as a unique material processing and analysis technique, provides distinct advantages over nanosecond laser ablation. Remote chemical analysis with fs-laser filament ablation has been demonstrated [4,14,15,16,17]
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