Study on Laser-Induced Optical Dielectric Film Material Damage by Short-Laser Pulse

Multi-photon ionization (MPI) and avalanche ionization (AI) have become main ionization mechanism of laser-induced optical dielectric film material damage, the different effects of MPI and AI for longer and shorter pulse are also discussed respectively. Based on Stuart et al.´s model equation and by means of numerical method, this paper has studied the interrelation of laser threshold intensity (I_th) versus laser pulse duration (τ) and damage threshold fluence (F_th) versus τ , and the effect of MPI and AI versus τ, studied electron density evolution in fused silica dielectric films induced by single-pulse laser. The results show that for fused silica film, for longer pulse duration τ, AI plays leading role and MPI serves for production of seed electrons for AI; for shorter duration τ, MPI predominates the prophase of the pulse duration. After stable MPI established, AI will exceed MPI and dominate the later period.