Study of laser ablation using nano-second laser pulses

In this paper, the laser ablation process based on the irradiation of nanosecond pulsed lasers on a copper target surface in the presence of Helium gas is studied. The dynamical behaviors of the generated plasma in the helium gas and evaporated copper at the atmospheric pressure are examined using a laser pulse, laser wavelength of and intensity of 7×1010W/cm2. A one-dimensional thermal model is used and, the numerical results show that, if the ionization and laser absorption processes in plasma plume are considered, the plume dynamics is strongly affected. It is seen that, the ionization at the copper surface will be increased during the laser pulses irradiation. On the other hand, the ionization degree for both the copper and helium is significantly varied according to their atomic structure. Moreover, for laser intensity in the range of 108 to 5×109W/cm2, the laser ablation is not occurred. The laser ablation threshold is about 5×109W/cm2. The first order ionization for copper is the dominant process in the proximity of both the target surface and mixed layer. On the other hand, in the plasma core, the second order ionization of copper is dominant. Besides, it is shown that, in the proximity of the target surface, the influences of photoionization and reverse Bremsstrahlung absorption for the electron-neutral are higher. In addition, the target parameters, including melt depth, evaporation depth and rate, plasma density, helium gas density, expansion velocity, plasma temperature and laser intensity reaching the copper target surface are studied.