The investigation of optical characteristics of metal target in high power laser ablation

In this work, the formulas for the absorption coefficient and the absorptivity depending on target temperature are derived from Maxwell Equations and the Lambert–Beer's law. A new theoretical model of laser ablation considering the temperature dependence of the absorption coefficient and the absorptivity has been developed. Then, as an example of Copper target, a finite difference method is employed to simulate the space-dependent and time-dependent absorption coefficient, absorptivity and temperature, as well as the time-dependent melt depth. The temperature evolution is compared with the result obtained from the heat conduction model taking the absorption coefficient and the absorptivity as constants. It is shown that the time-dependent absorption coefficient and absorptivity play an important role during the radiation of laser. Our calculated melt depth evolution is in better agreement with the experimental data than the result of the heat conduction model that regards the absorption coefficient and absorptivity as constants. Meanwhile, the corresponding physical mechanism is analyzed theoretically in detail.