Theoretical Simulation Studies Of Interactions Process Between Nanosecond Pulse Laser And Silicon Target

The interactions between nanosecond pulse laser with medium and low power density(I?5.0×10~8 W/cm~2 and materials involves the phase change of the target,the deposition of laser energy inside the target,the formation of the Knudson layer,plasma shielding,and the radiation and dynamical evolution of the plasma.In order to understand the process and theoretically reconstruct the entire process of the interaction between nanosecond pulse laser and material,which can not only analyze the dynamics evolution characteristics of the target and plasma,but also provide important guidance and support for the further development of important application fields,for example,the laser-induced breakdown spectroscopy technology and pulsed laser deposition technology.Based on the heat conduction equation,hydrodynamics equations and radiation transport equation,we have developed a two-dimensional axisymmetric radiation hydrodynamic model for studying the interactions process between nanosecond pulse laser and materials.The interactions have been fully considered among laser,target,and plasma in this model.The dynamical evolution of the plasma includes the contribution of various microscopic atomic process,real gas approximation(that is,the internal energy of plasma includes the thermal energy of electrons/atoms and ions,the ionization energy of atoms/ions,and the excitation energy of atoms/ions which is a precise description of the plasma internal energy has been adopted.This model can be applied to study the entire interaction process between nanosecond pulse laser and materials,which is helpful to understand the dynamics evolution of the target materials and dynamical evolution characteristics of plasma.In this thesis,a two-dimensional axisymmetric radiation hydrodynamics model which has been verified by various numerical calculations.The following work has been carried out based on the pulse laser(which the laser action parameters include the power density is 5.0×10~8 W/cm~2 and the wavelength is 1064 nm ablation solid silicon target where located in a vacuum environment:(1 The temperature distribution inside the target is simulated during the laser pulse ablation,and the temperature distribution is analyzed;(2 The time evolution profile of the target surface temperature,the plasma Mach number near the target surface and the laser transmissivity are given.The effect of the plasma shielding on the temperature distribution of the target surface is analyzed,the evaporation/condensation of the target surface is discussed in detail,and the coupling relationships among the target surface temperature,the plasma Mach number and the laser transmissivity are given in this paper.It is noted that the dynamical evolution process of the target surface can be divided into three processes:sonic evaporation,subsonic evaporation and subsonic condensation;(3 the distribution of plasma temperature,the particle number density and expansion velocity along the z-axial are obtained during laser ablation.The characteristics of dynamical evolution of plasma in vacuum are analyzed,and the coupling effect between the dynamics evolution of the target materials and the dynamics evolution of the plasma has been discussed.It is confirmed that the main absorption mechanism of plasma,such as inverse bremsstrahlung radiation,has played an important role for dynamics evolution of plasma;(4 The distribution of the internal energy of the plasma,which is consist of thermal energy,ionization energy and excitation energy,has been given,and an important conclusion which is the contribution of the excitation energy in the plasma internal energy cannot be ignored during the laser ablation...