Numerical FDTD-based simulations and Raman experiments of femtosecond LIPSS.

The article describes the results of finite-difference time-domain (FDTD) mathematical modeling of electric field strength distribution near the gold laser-induced periodic surface structures (LIPSS). Both theoretical and experimental results have been described for two fabricated morphologies: round «hill-like» and grating structures. The structures were fabricated by using a femtosecond Yb-fiber laser with a wavelength of λ=1032 nm, pulse duration τ=280 fs, and repetition rate υ=25 kHz. Morphological properties of the surfaces have been investigated by means of scanning electron microscopy (SEM). The plasmonic activity was analyzed by means of the surface-enhanced Raman spectroscopy (SERS) technique. FDTD-calculated electric field values were converted into the electromagnetic field enhancement coefficient and the theoretical SERS intensity. The prospects of the theoretical approach for LIPSS to evaluate optimal field amplification and light scattering parameters has been shown. The presented approach could be applied as a basis for performing the methods of controlled synthesis for LIPPS.