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

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.