  The efficiency of light coupling to surface plasmon polariton (SPP)
represents a very important issue in plasmonics and laser fabrication of
topographies in various solids. To illustrate the role of pre-patterrned
surfaces and impact of laser polsarisation in the excitation of electromagnetic
modes and periodic pattern formation, Nickel surfaces are irradiated with
femtosecond laser pulses of polarisation perpendicular or parallel to the
orientation of the pre-pattern ridges. Experimental results indicate that for
polarisation parallel to the ridges, laser induced periodic surface structures
(LIPSS) are formed perpendicularly to the pre-pattern with a frequency that is
independent of the distance between the ridges and periodicities close to the
wavelength of the excited SPP. By contrast, for polarisation perpendicular to
the pre-pattern, the periodicities of the LIPSS are closely correlated to the
distance between the ridges for pre-pattern distance larger than the laser
wavelength. The experimental observations are interpreted through a multi-scale
physical model in which the impact of the interference of the electromagnetic
modes is revealed.
