Interaction of ultrashort laser pulse with metals is considered. Ultrafast heating in our range of absorbed fluences Fabs > 10 mJjcm2 transfers matter into two-temperature (2T) state and induces expressed thermomechani cal response. To analyze our case, where 2T, thermomechanical, and multidimensional (formation of surface
structures) effects are significant, we use density functional theory (DFT), solutions of kinetic equations in τ- approximation, 2T-hydrodynamics, and molecular dynamics simulations. We have studied transition from light absorption in a skin layer to 2T state, and from 2T stage to hydrodynamical motions. We describe (i) formation of very peculiar (superelasticity) acoustic wave irradiated from the laser heated surface layer and (ii) rich com plex of surface phenomena including fast melting, nucleation of seed bubbles in hydrodynamically stretched fluid, evolution of vapor-liquid mixture into very spatially extended foam, mechanical breaking of liquid membranes in foam (foam disintegration), strong surface tension oscillations driven by breaking of membranes, non-equilibrium freezing of overcooled molten metals, transition to nano-domain solid, and formation of surface nanostructures.
A theoretical model is developed for the interaction of intense femtosecond laser pulses with solid targets on
the basis of the two-temperature equation of state for an irradiated substance. It allows the description of the
dynamics of the plasma formation and expansion. Comparison of available experimental data on the amplitude
and phase of the complex reflection coefficient of aluminum with the simulation results provides new information
on the transport coefficients and absorption capacity of the strongly coupled Al plasma over a wide range of
temperatures and pressures.
We model an interaction of femtosecond laser pulses (800 nm, 100 fs, 10E12-10E14 W/cm2) with metal targets (Al, Au, Cu and Ni). A detailed analysis of laser-induced phase transitions, melting wave propagation and material decomposition is performed using a thermodynamically complete two-temperature equation of state with stable and metastable phases. Material evaporation from the surface of the target and fast melting wave propagation into the bulk are observed. On rarefaction the liquid phase becomes metastable and its lifetime is estimated using the theory of homogeneous nucleation. Mechanical fragmentation of the target material at high strain rates is also possible as a result of void growth and confluence. In our simulation several ablation mechanisms are observed but the major output of the material is found to originate from the metastable liquid state. It can be decomposed either into a liquid-gas mixture in the vicinity of the critical point, or into droplets at high strain rates and negative pressure. The simulation results correlate with available experiments.
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