Warm dense matter in extremely small volume - Hydrodynamics of nanofilms triggered by laser irradiation at diffraction limit
Abstract
Modern laser techniques combine sophisticated manipulations of a photon bunch with the refined target design. The photon bunch of a femtosecond (fs) laser pulse (duration ∼ 100 fs) is just tens microns long (along a laser ray) and one micron thick (in direction transverse to the ray) when it is focused in the diffraction limited regime onto a target. Here the considered targets are films of different thicknesses (from tens nanometers, nm, to 100s nm). Also we compare pulse durations from 0.1 ps to tens of ps. In case of ultrashort laser action there is (i) an ultrafast isochoric transfer of initially solid metal into warm dense matter (WDM) state and (ii) after that molten metal returns back (more slowly) to a crystal (re-solidification finalizes processes initiated at any pulse duration). To study the evolution of these targets under such illumination conditions, a simulation package including two-temperature (2T) (2T - because immediately during and for some time after a fs pulse the electrons are much hotter than the lattice - thus two temperatures different for electrons and ions appear) 1D hydrodynamics code (2T-HD code) and 3D molecular dynamics (MD) code combined with Monte Carlo (MC) method (MD-MC code) are utilized. MC method allows us to take into account significant thermal conductivity of metal, which is important for cooling and re-crystallization of molten matter. The observed processes, including absorption, melting, capillary dynamics of hot liquid and its freezing into solitary nanostructure, produced by such laser electromagnetic fields, are discussed.
- Publication:
-
Shock Compression of Condensed Matter - 2017
- Pub Date:
- July 2018
- DOI:
- 10.1063/1.5045044
- Bibcode:
- 2018AIPC.1979s0002I