Metal Ablation by ps-Laser-Pulses: A Hybrid Simulation

Trennlinie

Boundary condition

We use a pressure-transmitting boundary condition for molecular-dynamics simulations in the last four monolayers of a copper crystal; and otherwise lateral periodic boundary conditions.  The new boundary condition - the teminating zone - prevents a pressure wave reflection, this is shown in the next figure.


t = 0.5       1.0         1.5         2.0         2.8         3.2          4.0         10.0 ps

The compressive pressure wave (red colored) travels with the velocity of sound through the crystal. After 3.2 ps the wave reaches the terminating zone, where calculation of the forces is changed. The high pressure is reduced to the nominal crystal pressure. The local pressures is in units of the bulk modulus, B=137 GPa.

A Hybrid Simulation

Motivation

Method

Molecular-dynamics (MD): Finite-difference scheme (FD):


Coupling:


System:

Laser ablation at the fluence 170mJ/cm2

a) Pressure

t = 29.4     30.4       31.4       32.4       33.4       34.4       35.0      35.8 ps

b) Temperature

t = 29.4     30.4       31.4       32.4       33.4       34.4       35.0      35.8 ps

Atomistic view of part of the laser-irradiated solid, at a time t = 32 ps, immediately after ablation occurred. Cross sections through the simulation volume (height 6 nm, width 2.1 nm, thickness 1 nm) are shown at various times after laser irradiation at a depth of 23 nm. Atoms are colored (a) according to their local pressures, in units of the bulk modulus, B = 137 GPa, and (b) according to their local temperature, in units of the melting point of copper, Tm = 1358 K. The local temperature of an atom is defined as the average kinetic energy of all atoms around the central atom within a radius of 6.2 A (cutoff of the interaction potential), in the center of mass system. Analogously, local pressures are defined as an average over the atomic virials.

Animation of the entire simulation (170mJ/cm2): 50 ps simulation time, 0.5 ps laser pulse, 14 nm penetration depth. Single spallation Animation of the entire simulation (400mJ/cm2):  50 ps simulation time, 0.5 ps laser pulse,  14 nm penetration depth. Multiple spallation.

Results


Trennlinie

eMail: C. Schäfer
Prof. Dr. H. M. Urbassek
last reviewed: 29.08.2001
last updated: 29.08.2001