Dynamics of plasma expansion and shockwave formation in femtosecond laser-ablated aluminum plumes in argon gas at atmospheric pressures

Abstract

Plasma expansion with shockwave formation during laser ablation of materials in a background gasses is a complex process. The spatial and temporal evolution of pressure, temperature, density, and velocity fields is needed for its complete understanding. We have studied the expansion of femtosecond (fs) laser-ablated aluminum (Al) plumes in Argon (Ar) gas at 0.5 and 1 atmosphere (atm). The expansion of the plume is investigated experimentally using shadowgraphy and fast-gated imaging. The computational fluid dynamics (CFD) modeling is also carried out. The position of the shock front measured by shadowgraphy and fast-gated imaging is then compared to that obtained from the CFD modeling. The results from the three methods are found to be in good agreement, especially during the initial stage of plasma expansion. The computed time-and spaceresolved fields of gas-dynamic parameters have provided valuable insights into the dynamics of plasma expansion and shockwave formation in fs-pulse ablated Al plumes in Ar gas at 0.5 and 1 atm. These results are compared to our previous data on nanosecond (ns) laser ablation of Al [S. S. Harilal et al., Phys. Plasmas 19, 083504 (2012)]. It is observed that both fs and ns plumes acquire a nearly spherical shape at the end of expansion in Ar gas at 1 atm. However, due to significantly lower pulse energy of the fs laser (5 mJ) compared to pulse energy of the ns laser (100 mJ) used in our studies, the values of pressure, temperature, mass density, and velocity are found to be smaller in the fs laser plume, and their time evolution occurs much faster on the same time scale. The oscillatory shock waves clearly visible in the ns plume are not observed in the internal region of the fs plume. These experimental and computational results provide a quantitative understanding of plasma expansion and shockwave formation in fs-pulse and ns-pulse laser ablated Al plumes in an ambient gas at atmospheric pressures. V

Expansion dynamics of ultrafast laser produced plasmas in the presence of ambient argon

“…32 At these pressure levels, the plume is found to be decelerated even at very earlier times of its evolution which leads to collisional excitation and confinement and eventually the plume length is limited to a few mm. By comparing spectrally integrated images with spectrally filtered images, it can be inferred that spectrally integrated images follow the features and trends of emission from Cu I and Zn I species.…”

“…Recent CFD modeling results also confirmed that the oscillatory internal shock waves routinely seen in ns laser ablation plumes were absent in the case of fs LA plumes at atmospheric pressure levels. 32 ICCD images obtained at different pressure levels showed significant changes in the plume's morphology and hence the aspect ratios (Fig. 1).…”

“…For ns LPPs, the plume expands into a heated ambient environment with longer plasma persistence resulting in a lesser influence of the ambient gas for ns LPP. 31 Recent computational fluid dynamics (CFD) study of ns and fs laser ablation plumes at atmospheric pressure levels 32,33 showed oscillatory plume structures for ns LA while internal shock waves were absent in the case of fs LA.…”

Shock Waves in Laser-Induced Plasmas

“…Accurate numerical simulations of the process of shock wave propagation in gases were performed by Dors and Parigger [11] and successfully compared with high-speed, high-resolution shadowgraph techniques. Other important computational and experimental studies on laser-induced shock waves were performed by Harilal and coworkers [12][13][14], in the framework of extensive and articulated research devoted to the study of the expansion of the laser plume in different ambient gases and experimental configurations [15][16][17][18][19][20]. In a recent paper, Hermann et al [21] studied the evolution of the pressure in a steel plasma, acquiring its emission spectrum and successfully comparing the experimental data with the results of computer simulations.…”

Complex Systems with Self‐Elimination of Dissipation with Implication in Bio‐Structural Behavior Via Nondifferentiability

“…Once the ambient pressure increases, the plume evolution is determined by the interactions of the laser plasma and ambient gas [25].…”