  Ultrafast laser material processing has received significant attention due to
a growing need for the fabrication of miniaturized devices at micro- and
nanoscales. The traditional phenomenological laws, such as Fourier's law of
heat conduction, are challenged in the microscale regime and a hyperbolic or
dual phase lag model should be employed. During ultrafast laser interaction
with metal, the electrons and lattices are not in equilibrium. Various
two-temperature models that can be used to describe the nonequilibrium heat
transfer are presented. A semi-classical two-step heating model to investigate
thermal transport in metals caused by ultrashort laser heating is also
presented. The main difference between the semiclassical and the
phenomenological two-temperature models is that the former includes the effects
of electron drifting, which could result in significantly different electron
and lattice temperature response from the latter for higher-intensity and
shorter-pulse laser heating. Under higher laser fluence and/or short pulse, the
lattice temperature can exceed the melting point and melting takes place. The
liquid phase will be resolidified when the lattice is cooled by conducting heat
away. Ultrafast melting and resolidification of the thin gold film and
microparticles were investigated. At even shorter pulse width, femtosecond
laser heating on metals produces a blasting force from hot electrons in the
sub-picosecond domain, which exerts on the metal lattices along with the
non-equilibrium heat flow. Our work that employs the parabolic two-step heating
model to study the effect of the hot-electron blast in multi-layered thin metal
films is also presented.
