  We present a theoretical study of the ultrafast electron dynamics in
transition metals using ultrashort pulsed laser beams. The significant
influence of the contribution of the dynamics of produced nonthermal electrons
to electron thermalisation and electron-phonon interaction is thoroughly
investigated within a range of values of the pulse duration (i.e. from 10fs to
2.3ps). The theoretical model elaborates firstly on possible transient changes
of optical parameters during irradiation due to the presence of the
non-equilibrium electrons and the modification of the electron distribution
function in a material characterized by a variable electron density of states
around the Fermi energy. The model correlates the role of nonthermal electrons,
relaxation processes and induced stress-strain fields. Simulations are
presented by choosing Nickel (Ni) as a test material to compute electron-phonon
relaxation time due to its large electron-phonon coupling constant that expects
to reveal more conclusively the influence of the non-equilibrium electrons. We
demonstrate the consideration of the above factors leads to significant changes
compared to the results the traditional Two Temperature Model (TTM) provides.
The proposed model predicts a substantially (~33%) smaller damage threshold and
a large increase of the stress (~20%, at early times) which firstly underlines
the role of the nonthermal electron interactions and secondly enhances its
importance with respect to the precise determination of laser specifications in
material micromachining techniques.
