Grating-assisted fabrication of sub-wavelength ripples during femtosecond laser processing of dielectrics

During the formation of sub-wavelength ripples, the initial surface plasmon(SP)-laser interference plays an important role. In this Letter, the effects of grating structures on the distribution of the absorbed laser intensity,SP-laser coupling, free electron distributions, and ablation shapes are investigated by the plasma model, taking into consideration both the laser wave-particle duality and the transient localized changes of material properties.The simulation results show that the grating structures can strongly enhance the energy absorption and SP-laser coupling, which makes the fabrication of sub-wavelength ripples more efficient. It is also found that the ablation shapes, in terms of ablation depths and sub-wavelength ripples periods, are strongly related to the grating structures, which can be used to control micro/nanostructures precisely and uniformly.