Time-resolved dynamics of nanosecond laser-induced phase explosion

Abstract

Visualization of Nd : YAG laser ablation of aluminium targets was performed by a shadowgraph apparatus capable of imaging the dynamics of ablation with nanosecond time resolution. Direct observations of vaporization, explosive phase change and shock waves were obtained. The influence of vaporization and phase explosion on shock wave velocity was directly measured. A significant increase in the shock wave velocity was observed at the onset of phase explosion. However, the shock wave behaviour followed the form of a Taylor–Sedov spherical shock below and above the explosive phase change threshold. The jump in the shock wave velocity above phase explosion threshold is attributed to the release of stored enthalpy in the superheated liquid surface. The energy released during phase explosion was estimated by fitting the transient shock wave position to the Taylor scaling rules. Results of temperature calculations indicate that the vapour temperature at the phase explosion threshold is slightly higher than the critical temperature at the early stages of the shock wave formation. The shock wave pressure nearly doubled when transitioning from normal vaporization to phase explosion.

Nanosecond Laser Ablation: Mathematical Models, Computational Algorithms, Modeling

“…Primary attention is paid to model the dynamics of phase explosion of liquid phase of aluminum and the expansion of its fragments in the air, since explosive boiling is considered to be one of the most effective thermal mechanisms of ns laser ablation of materials. Various aspects of this problem have been studied in a number of theoretical and experimental studies [43][44][45][46][47][48][49][50][51][52][53][54][55][56], but there is still no consensus on the mechanism of the phase explosion in metals. In order to obtain detailed information on interaction of heterogeneous and homogeneous mechanisms and data on laser plume morphology, simulation of laser heating, melting, surface evaporation, and evolution of plume in the vapor-gas medium is performed within the framework of new hydrodynamic model with temperature dependences of material properties of the target and explicit tracking of interphase boundary fronts, contact boundary, and shock wave.…”

“…In other experimental and theoretical studies of the interaction of ns-laser pulses with an intensity of 10 7 -10 8 W/cm 2 with metallic targets, the results of the appearance of metal-dielectric transitions accompanied by the formation of transparency waves are reported [53,54,85,[88][89][90][91].…”

Imaging spectroscopy of polymer ablation plasmas for laser propulsion applications

“…4 Relative to PLA in vacuum, additional physical processes occur in the presence of background gas, including shock wave creation and propagation, 5 plasma confinement, 6 and charge exchange during plasma formation and expansion. Many techniques have been employed to characterize the shock wave, including fast photography, 6 shadowgraphy, 7 interferometry, 8,9 time-gated emission imaging, 10,11 or spectroscopy. 12 Ablation of a broad range of materials has been investigated, spanning liquids to multi-component solid systems, under vacuum and in the presence of different pressures of both inert and reactive background gases, using a wide variety of laser types.…”

Development of numerical model to investigate the laser driven shock waves from aluminum target into ambient air at atmospheric pressure and its comparison with experiment

“…During laser-target interaction different physical processes occur like target heating, melting, evaporation, ionization, plasma formation occur. While after termination of laser pulse an adiabatic expansion of the plasma, SW expansion in ambient air take place [3][4][5][6][7][8][9]. All these processes lead to complexity of the problem.…”

“…All these processes lead to complexity of the problem. Experimental and numerical studies on laser ablative shock waves (LASW) of aluminum in vacuum, inert gas atmosphere have focused on plume formation, plume structure and its dynamics [3,5], phase explosion [6], SW formation, propagation and confinement [7], geometrical transition in SW during its evolution [8,9]. While very few reports are available on the expansion of SW in ambient atmospheric air.…”