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.
Moleculardynamics (MD):Laser ablation at the fluence 170mJ/cm^{2}Finitedifference scheme (FD):
 Cu crystal, l=72 nm deep, 2.2 nm wide, with periodic boundary conditions
 Nonreflecting boundary conditions [Zhigilei and Garrison, 2000] are used at the bottom side, x=l, to prevent pressure wave reflection.
 electron heat transport down to a depth of L=400 nm
 electron heat conductivity dependent on electron and atom temperatures [Anisimov and Rethfeld, 1996]
Coupling:
 electronphonon coupling introduced as a velocitydependent force in MD [Häkkinen and Landman, 1993]
 electronphonon coupling introduced as a gain/lossterm in FD
 atomic heat calculated in FD and coupled to electron heat between l < x < L
System:
 0.5 ps irradiation of Cu with 250 nm laser, fluence between 100 and 450 mJ/cm^{2}. Laser penetration depth: lambda=14 nm.
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 laserirradiated 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, T_{m} = 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/cm^{2}): 50 ps simulation time, 0.5 ps laser pulse, 14 nm penetration depth. Single spallation Animation of the entire simulation (400mJ/cm^{2}): 50 ps simulation time, 0.5 ps laser pulse, 14 nm penetration depth. Multiple spallation.

last reviewed: 29.08.2001
last updated: 29.08.2001 