  The accurate calculation of laser energy absorption during femto- or
picosecond laser pulse experiments is very important for the description of the
formation of periodic surface structures. On a rough material surface, a crack
or a step edge, ultrashort laser pulses can excite surface plasmon polaritons
(SPP), i.e. surface plasmons coupled to a laser-electromagnetic wave. The
interference of such plasmon wave and the incoming pulse leads to a periodic
modulation of the deposited laser energy on the surface of the sample. In the
present work, within the frames of a Two Temperature Model we propose the
analytical form of the source term, which takes into account SPP excited at a
step edge of a dielectric-metal interface upon irradiation of an ultrashort
laser pulse at normal incidence. The influence of the laser pulse parameters on
energy absorption is quantified for the example of gold. This result can be
used for nanophotonic applications and for the theoretical investigation of the
evolution of electronic and lattice temperatures and, therefore, of the
formation of surfaces with predestined properties under controlled conditions.
