Abstract
Shock-wave generation by ultrashort laser pulses opens new doors for study of hidden processes in materials happened at an atomic-scale spatiotemporal scales. The poorly explored mechanism of shock generation is started from a short-living two-temperature (2T) state of solid in a thin surface layer where laser energy is deposited. Such 2T state represents a highly non-equilibrium warm dense matter having cold ions and hot electrons with temperatures of 1-2 orders of magnitude higher than the melting point. Here for the first time we present results obtained by our new hybrid hydrodynamics code combining detailed description of 2T states with a model of elasticity together with a wide-range equation of state of solid. New hydro-code has higher accuracy in the 2T stage than molecular dynamics method, because it includes electron related phenomena including thermal conduction, electron-ion collisions and energy transfer, and electron pressure. From the other hand the new code significantly improves our previous version of 2T hydrodynamics model, because now it is capable of reproducing the elastic compression waves, which may have an imprint of supersonic melting like as in MD simulations. With help of the new code we have solved a difficult problem of thermal and dynamic coupling of a molten layer with an uniaxially compressed elastic solid. This approach allows us to describe the recent femtosecond laser experiments.
Highlights
Shock compression of solids was being studied intensively last several decades [1]
The Hugoniot Elastic Limit (HEL) uniaxially deformed state becomes impossible - instead, isotropization of stresses and deformations takes place. For such metals as aluminum, nickel, and so on, the usual values of HEL are small - this means that an elastic shock wave (SW) driven by piston at a stress near HEL has velocity Del only 1 − 2% higher than elastic sound speed cel
This is why a strong elastic SW firstly observed in the excellent pump-probe experiments with femtosecond lasers done by Evans et al [7] and Gahagan et al [8] was not recognized as an elastic wave
Summary
Shock compression of solids was being studied intensively last several decades [1]. Hugoniot Elastic Limit (HEL) is a key concept in this branch of science. Experiments [2, 3, 5, 6] and simulations [2, 4, 9, 10] (i) reveal that uniaxially compressed lattice survives under huge stresses, (ii) describe elastic branches 1 of Hugoniot adiabats at high volume compressions and pressures, and (iii) discover the dynamic coupling of elastic and plastic SW [10]. Well defined temporal synchronization of pump and diagnostics, and high temporal resolution allow to observe powerful p ∼ 10 GPa pure elastic (no accompanying plastic SW) SW in experiments [2, 3, 5, 6].
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