Numerical investigation of ultrashort laser interaction with dielectric materials based on a plasma-temperature combined model

Numerical study of ultrashort laser-induced ablation of dielectric materials is presented based on a one-dimensional plasma-temperature model. Plasma dynamics including photoionization, impact ionization, relaxation and electronic diffusion are considered through an improved single-rate equation. Material decomposition is captured by a temperature-based ablation criterion. Dynamic description of ablation process has been achieved through instant material removal. Behaviors of laser-induced ablation threshold, transient optical properties and ablation depth have been investigated with respect to incident fluence and pulse duration. Good agreements are shown between numerical predictions and experimental observations. Fast increase of ablation depth, followed with saturation, is observed with the increase of the incident fluence. The ablation efficiency decreases with fluence after reaching the peak value at the fluence twice of the ablation threshold. Material processing at low laser fluence and ultrashort pulse duration is proved to be able to provide higher ablation efficiency and reduced thermal damage. The divergence of tightly focused Gaussian beam in transparent materials has been revealed to significantly affect the ablation process, particularly at high laser fluence. This effect is found to be negligible in laser processing of metals.