Numerical Study On The Effects Of Laser Mode On The Ablation Of Metallic Targets

Laser ablating materials is a complex physical and chemical process. Its effects are affected by laser, material and environments. Taking the aluminum, magnesium and titanium as the studied objects, we calculated their temperature fields and ablated threshold with the self-compiled program when they were irradiated by 1.064?m laser. The works done in this thesis are:(1) Taking thermal conduction as basis and with smoothed particle hydrodynamics method, we compiled the program used for laser ablating materials in two-dimensional cylindrical coordinates. In this program, all the processes, such as the change of reflectance on the material surface with temperature and wavelength, the phase transition process such as melt and gasification, the boundary conditions and the effects of air convection are considered, are considered.(2) Meanwhile, Basing on the contact algorithm, which can just be used for same size SPH particles, early presented by others, we generalized this algorithm to different size SPH particles and used this in the laser-ablating program.(3) With the self-compiled laser-ablating program, we carried out the numerical study of the ablating threshold of aluminum, magnesium and titanium. The peak power, the mean power, the repetition frequency and duty ratio are considered in the research. The calculated results showed that the repetition frequency and duty ratio has more influence on the ablating effects. The smaller the repetition frequency and duty ratio are, the less time to ablate the material is needed. During 1 minute, to ablate through the materials with 2cm thickness, the minimum mean power for aluminum, titanium and magnesium are 5000 W, 1500 W and 2500 W respectively. Of the three metallic materials, the titanium is the easiest one to be laser-ablated.