Rarefaction shock wave:  Formation under short pulse laser ablation of solids

Abstract

We investigate formation, dynamics, and decay of the rarefaction shock wave under the conditions of ultrashort pulse laser ablation of solids. On the basis of the Euler equation and the van der Waals equation, we consider the planar and spherical expansion into vacuum matter heated instantaneously above the thermodynamic critical temperature. When the expansion occurs along an abnormal adiabat, in a part of which ( partial differential(2)p/ partial differentialv(2))/(S)<0, a rarefaction shock wave moving toward the target is formed. After its reflection from the nonvaporized material of the target, a thin dense layer of the expanding material is found to be formed. We suggest that this is the explanation for interference patterns observed experimentally above laser ablated surfaces. It has been speculated that the rarefaction shock wave may be formed on nova outbursts.

Nonlinear hydrodynamic waves: Effects of the equation of state

“…It has been shown that negative nonlinearity can be realized for materials with different EOS [24]. Recently [15] we have shown that, for the three-parametric modification of the van der Waals EOS [25,26] which accurately describes a wide variety of substances, the RSW behaves differently as compared to the case with the classic van der Waals EOS [2], which is worthy of detailed study.…”

“…Recently it has been shown that, under ultrashort-pulse laser ablation of solids, the rarefaction shock wave (RSW) can be formed in laser-induced plumes [1,2]. An intriguing picture of the formation of a compressed layer in the ablation products expanding in a vacuum has been revealed after RSW reflection from a nonvaporized target surface.…”

“…However, the RSW appears to be a fairly general phenomenon which it is possible to observe in expanding and stationary plasmas [3][4][5], particularly in magnetized [6,7] and optically thin radiative plasma [8], in a nonequilibrium vibrationally excited gas [9], and in binary gas mixtures [10]. It has been speculated that the RSW may be observed under implosions of internal confinement fusion pellet materials [11] and in stellar envelopes [2]. A fascinating picture is formed in the transonic flows of inviscid fluids with regions of negative and positive nonlinearities [12,13].…”

“…A fascinating picture is formed in the transonic flows of inviscid fluids with regions of negative and positive nonlinearities [12,13]. It has been shown that in spherical geometry the RSW effects can be even more pronounced than in planar geometry [2,14,15]. It has been suggested that the effects related to the RSW's may prove to be important for practical use [16,17] in postponing the phenomenon of choking of real gas flows in pipes [16] and improving organic Rankine cycle engines [17] due to weakening shock-wave impacts.…”

Expansion shock waves in the implosion process from a time-reversible molecular-dynamics simulation of a dual explosion process

“…1 ͒ As predicted by Zel'dovich, 2 analyzed by Thompson,3,4 and clarified experimentally by Borisov, 5 an expansion shock wave can be generated in the vicinity of the "liquid-vapor" critical point, or in some porous solids undergoing a phase transition at high pressures, etc. [6][7][8][9][10] For example, near the liquid-vapor critical point, the value ‫ץ͑‬ 2 p / ‫ץ‬v 2 ͒ s becomes negative for a substance with a reasonably high specific heat c v ͑where p, v, and s represent the pressure, specific volume, and entropy, respectively͒ and, therefore, expansion shock waves can be generated under such specific conditions. 9 In a "gaseous" medium corresponding to normal fluids, however, the value ‫ץ͑‬ 2 p / ‫ץ‬v 2 ͒ s is positive.…”