Nanopatterning of the dielectric surface by a pair of femtosecond laser pulses of different colors through a monolayer of microspheres

This paper considers the nanostructuring of the surface of dielectrics under the effect of two successive femtosecond laser pulses, one of the fundamental frequency (FF) and the other of the second harmonic (SH) of a Ti:sapphire laser, through a layer of polystyrene microspheres 1 µm in diameter, which act as microlenses. Polymers with strong (PMMA) and weak (TOPAS) absorption at the frequency of the third harmonic of a Ti:sapphire laser (sum frequency FF + SH) were used as targets. Laser irradiation led to the removal of microspheres and the formation of ablation craters with characteristic dimensions of about 100 nm. Depending on the variable delay time between pulses, the resulting structures differed in their geometric parameters and shape. Based on statistical processing of the depths of the obtained craters, the optimal delay times for the most effective structuring of the surfaces of these polymers was found.