Ultrashort laser-matter interaction at moderate intensities: two-temperature relaxation, foaming of stretched melt, and freezing of evolving nanostructures

Abstract

Interaction of ultrashort laser pulse with metals is considered. Ultrafast heating in our range of absorbed fluences F abs > 10 mJ/cm 2 transfers matter into two-temperature (2T) state and induces expressed thermomechanical 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 complex 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.

In situ thermal characterisation and filamentary modification in Polymethylpentene

“…This inscription opens up a method to construct 2D or 3D structures in transparent materials. The inscription can employ physical and chemical mechanisms, such as the thermomechanical effect [24], optical breakdown [25], filamentation [26], incubation [27], and photo-exciting chemical reactions [17] to conduct the inscription. The inscription can internally modify the material, producing a change in the refractive index [28].…”