Numerical Simulation Of Laser Ablation Of Solid Materials Caused By Mechanical Effects

When an intense laser beam is incident on a solid target, laser energy is absorption by ambient air and the surface layer of the target. Ambient air ionizes and becomes plasma, while part of the target rises in temperature,melts,vaporizes,ionizes and till becomes plasma. Hydrodynamics behavior of the vapor or plasma and the mechanical response in the target induced by laser irradiation compose the mechanical effects of laser irradiance on matter. Those mechanical effects have broad applications, such as laser shot peening, laser driven flyer, laser propulsion and clearing space debris, laser driven shockless compression, laser driven inertial confinement fusion (ICF), high pressure equation of state and dynamic material properties with high strain rate. A one-dimensional(1D) bulk absorption model to simulate the solid target ablated directly by the laser beam is presented, numerical simulation of the mechanical effects is performed with fluid dynamics theory and 1D Lagrange difference scheme.The mechanical effects of laser irradiance on matter was introduced, and the application was summarized. Hydrodynamics behavior of the vapor or plasma induced by laser irradiation has been described, including 1D steady flow of the target vapor,1D unsteady flow of low temperature vapor and high temperature plasma, laser supported combustion and detonation waves, laser induced ablation pressures and shock waves, which is the theoretical basis of the mechanical effects.Based on the introduction of laser energy deposition or absorption in matter, a bulk absorption model of the dynamic physical processes of laser target interaction was set up. The laser ablation processes of monolayer free target were simulated with a modified 1D Lagrange fluid dynamic code SSS. The calculated rear free surface velocity histories were consistent with the measured ones with the VISAR. The calculations gave the temperature, density, pressure, velocity and average ionization charge of different position and time and showed the basic physical patterns of laser ablation. The order of the calculated ablation pressures agreed with Phipps law.The accelerating process of laser-driven flyer plate has been simulated, the calculated results of the ablated thickness are in good agreement with the experimental results. Numerical simulation results show that higher velocity flyer is obtained by using thinner target or increasing the laser energy. On the basis of the simulation this paper analyzes the key factors which influence the flyer velocity. Experiments of measuring the impulse coupling to target irradiated by laser in vacuum by using the pendulum device were introduced. The experimental results showed that the mechanical coupling coefficient Cm firstly rose up then fell down with the increment of laser intensity, which was the characteristic of the formation process of plasma. Numerical calculation of impulse acting on the target in vacuum with different laser parameters is performed, the calculated results of Cm are in good agreement with the experimental results and Phipps'empirical value.In this paper, the background,advancement and operating principals of laser clearing space debris were introduced. According to the theory of momentum coupling of laser beams with matter and the development of laser device, we have analyzed the physical process of laser clearing space debris in detail. The estimates of the typical operating mode show that clearing space debris using ground-based laser system is practical.