This work analyzes microscopic radiation metal interactions in short-p
ulse laser heating processes and their effects on the material thermal
response. The radiation metal interactions are treated as a coupled t
wo-step process: (1) the absorption of photon energy by electrons and
(2) the subsequent heating of the metal lattice through electron-phono
n collisions. Key parameters, pulse duration to relaxation, relaxation
to diffusion, and heating intensity, are introduced to classify this
two-step heating regime and the conventional one-step heating regime.
In the two-step heating regime. the microscopic energy transfer among
photons, electrons and phonons enlarges the size of the heat-affected
region and lowers the peak metal lattice temperature rise significantl
y. The predicted transient reflectivity changes agree with sub-picosec
ond laser heating experiments.