Picosecond Laser Ablation Of Silicon And Laser-induced Plasma Diagnosis By Optical Emission Spectroscopy At Different Argon Pressures

Pulsed laser ablation is widely used in multiple fields.The evolution of laser induced plasma(LIP)is quite complicated.Fundamental studies of picosecond laser ablation with various background pressures are investigated both theoretically and experimentally here.The main work of this research are concluded as follows:1.A theoretical model for picosecond pulsed laser ablation of silicon target is pro-posed.Three main processes during ablation are discussesd:target absorption of laser energy,interaction between laser and plasma and the evolution of plasma.2.A two-dimensional hydrodynamic code POLLUX is used to simulate the ablation process of silicon with picosecond pulse laser in vacuum.The total number of electron reach the order of 10²⁴cm^-3within ten nanoseconds.Electron temperatures reach 50 e V within several hundred picoseconds,and spread around quickly after several nanoseconds.3.A self-designed spectral diagnostic system is designed and built.The evolution of LIP with different background gas pressures are tested.Ions in each charge state spread inside plasma with thier own velocity distributions.With increasing pressures,the veloc-ities of plasma plume declined obviously.But the total emission intensities are greatly enhanced.Si ions in high charge state interact with background gas and transfer from high energy states to relative ones.Meanwhile,shock waves are observed clearly.Stark broadening method is used to analyze the spectral line of Ar II and the electron densities are calculated.N_ereaches the order of 10¹⁶cm^-3and a bunch of electrons gather near the target.Through the above research,we can better understand the physical evolving mecha-nism of laser induced plasma with different background pressures,so as to better combine pulsed laser ablation technology with practical applications.