Experimental and computational study of complex shockwave dynamics in laser ablation plumes in argon atmosphere

• Published in: Physics of plasmas 2012-08, Vol.19 (8)
• Main Authors: Harilal, S. S., Miloshevsky, G. V., Diwakar, P. K., LaHaye, N. L., Hassanein, A.
• Format: Article
• Language: English
• Subjects: 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ABLATION; ARGON; ATMOSPHERIC PRESSURE; CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; COMPUTERIZED SIMULATION; CONTROLLED ATMOSPHERES; EMISSION; HYDRODYNAMIC MODEL; ICP MASS SPECTROSCOPY; LASER-PRODUCED PLASMA; NEODYMIUM LASERS; PHOTOGRAPHY; PLASMA CONFINEMENT; PLUMES; SHOCK WAVES
• ISSN: 1070-664X; 1089-7674
• DOI: 10.1063/1.4745867

We investigated spatio-temporal evolution of ns laser ablation plumes at atmospheric pressure, a favored condition for laser-induced breakdown spectroscopy and laser-ablation inductively coupled plasma mass-spectrometry. The 1064 nm, 6 ns pulses from a Nd:YAG laser were focused on to an Al target and the generated plasma was allowed to expand in 1 atm Ar. The hydrodynamic expansion features were studied using focused shadowgraphy and gated 2 ns self-emission visible imaging. Shadowgram images showed material ejection and generation of shock fronts. A secondary shock is observed behind the primary shock during the time window of 100-500 ns with instabilities near the laser cone angle. By comparing the self-emission images obtained using fast photography, it is concluded that the secondary shocks observed in the shadowgraphy were generated by fast moving target material. The plume front estimates using fast photography exhibited reasonable agreement with data obtained from shadowgraphy at early times ≤400 ns. However, at later times, fast photography images showed plume confinement while the shadowgraphic images showed propagation of the plume front even at greater times. The structure and dynamics of the plume obtained from optical diagnostic tools were compared to numerical simulations. We have shown that the main features of plume expansion in ambient Ar observed in the experiments can be reproduced using a continuum hydrodynamics model which provided valuable insight into the expansion dynamics and shock structure of the plasma plume.