Effects of two-color femtosecond pulses irradiation of polymer surface through the monolayer of dielectric microspheres

We consider irradiation of a polymer surface covered by the monolayer of the polystyrene microspheres by two femtosecond pulses of different colors (fundamental frequency (FF) and second harmonic (SH)) with variable delay between them. The polymer is transparent at the wavelength of the third harmonic (FF+SH). We show that, when irradiating the surface, changing the order of the pulses succession results in dominating either ablation or swelling of the irradiated spots. We discuss the laser swelling in terms of hydrodynamic model that is the formalization of the relaxation mechanism of this phenomenon in glassy materials.