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

Abstract

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.

Carbon-atom wires produced by nanosecond pulsed laser deposition in a background gas

“…The shock front is a region characterized by strong gradients of temperature, velocity and pressure, where clustering of the ablated species can occur in out-of-equilibrium conditions [39][40][41][42].…”

Desorption/ablation of lithium fluoride induced by extreme ultraviolet laser radiation

“…However, multidimensional numerical simulations of fl uid dynamics can bring yet unexplored insight into such complex physical phenomena. For example, shock-wave propagation after pulsed laser irradiation of Al targets under the atmospheric pressure conditions was studied by Harilal et al [8] employing unsteady solver of Navier-Stokes equations in a two-dimensional axially symmetric geometry.…”

Signal enhancement in collinear double-pulse laser-induced breakdown spectroscopy applied to different soils

“…The decrease of ambient gas density close to the target surface would lead to a decrease of laser shielding by the pre-plasma thereby determining an increase of the laser ablation and signal enhancement [10]. The shockwave front detaches from the plume front after few hundreds of ns and moves further, while the plume core gets stagnant at few mm from the plasma surface depending on the laser pulse energy [10,47]. At higher interpulse delays (>500 ns), optimal rarified regions are generated which lead to a signal enhancement mostly due to increased mass ablation.…”