Periodic surface structure formation on silicon surfaces by irradiation of single and multiple femtosecond laser pulses

Laser-induced periodic surface structures (LIPSS) were obtained on Si substrates using various number of ultrashort laser pulses with 266 fs pulse width at a 1030 nm wavelength. The obtained structures were investigated with SEM, EDS and optical spectroscopy techniques, then the obtained results were simulated by theoretical calculations. In the applied theoretical approach, the LIPSS formation is simulated by a semi-empirical model of interference of the incident laser beam with surface scattered electromagnetic waves generated at a rough surface, which includes excitation of surface plasmon polaritons (SPP) and accounts for the transient intrapulse changes in optical properties due to photo-excitation of a dense plasma of electron-hole pairs. The threshold for excitation of SPPs depends on the laser energy fluence, wavelength, polarization direction and the pulse number. We determine these thresholds from first principal calculation of the macroscopic dielectric function of the photo- excited solid.