Collaborators:
David Autrique (Physics, Univ. of Kaiserslautern, Germany),
Harihar Khanal (Math, Embry-Riddle Aeronautical Univ.,
Daytona Beach FL)
Developing seamless, thermodynamically consistent, hydrodynamic models of target heating/melting/vaporization, and of plasma formation and evolution, in laser ablation (LA) of metals by nanosecond lasers.
Laser ablation:
Several complex, tightly coupled physical processes occur in and just
above the target. The target heats up, melts and vaporizes. In the
Knudsen Layer, just above the target, the evaporated particles rapidly
equilibrate by collisions, get ionized and form a plasma. The plasma
absorbs laser energy, shielding the target, and attains very high
temperatures, velocities, species densities, and pressures.
As the plume cools, homogenous nucleation and recondensation result in
nanosized particles. Recoil pressures on the melt can cause melt motion
and melt expulsion forming larger particles.
Additional challenges in modeling laser ablation arise from: (a) extreme
space and time scales; (b) extreme gradients: temperature may rise to
thousands of degrees locally; (c) extreme variation in thermophysical
properties; (d) the need for extensive thermophysical data: T-dependent
density, heat capacity, thermal conductivity; phase diagram for solid,
liquid, vapor over the range 300 K to critical temperature (8000 K for
Cu); (e) the need for T-dependent and wavelength dependent optical data.
Approach:
Our formulation is based on Equations of State of the form
H = H(T, P, phase)
consistent with the thermochemistry of the material. It allows
full temperature (and/or pressure) dependence of thermophysical and
of optical properties, and can use available EOS data, up to critical
temperature. Thus, it can realistically describe all the phases of
real materials.
No a priori assumptions are made regarding phase formation,
thus simulations can reveal phenomena not expected a priori
(e.g. bimodal temperature
and pressure
evolution that may induce re-condensation).
The conservation laws are discretized by finite volumes, and
time-stepping can be explicit or implicit. For the Euler equations
in the plume, high resolution numerical schemes are used to
capture the (very) strong shocks.
Applications:
occur in diverse fields, from archaeology, chemistry, and medicine, to
environmental science, and, especially, in materials science.
Materials processing applications include: pulsed laser deposition,
nanoparticle manufacturing, micromachining, and chemical microanalysis.
Papers:
