Effect of variation of magnetic field on laser ablation depth of copper and aluminum targets in air atmosphere

摘要

We report on the effect of transverse magnetic field on laser ablation of copper and aluminum targets both experimentally and numerically. The ablation depth is found to increase with magnetic field from 0 to 0.3 T and decreases at a higher magnetic field (0.5 T). It is demonstrated that the nanosecond laser ablation is mainly due to melt ejection and it solely depends on the thermo-physical parameters of the material. The increase in ablation depth with magnetic field is attributed to the increase in heat transfer from the plasma to the target, vapor pressure, and shock pressure. The ablation due to melt ejection is also calculated using vapor pressure through simulation and compared with the experimentally measured depth. In the presence of magnetic field, we introduce the magnetic pressure in Clausius-Clapeyron vapor pressure equation to account for the combined effect of magnetic field and atmospheric pressure on the vapor pressure of plasma. The ratio of calculated ablation depth at 0.3 T with respect to the absence of magnetic field is close to the corresponding experimental depth ratios indicating that the laser ablation modeling in the present work is validated. As the magnetic field increases, we observed the scattered mass at the center and around the crater. The size of deposited mass at the center is found to decrease at higher magnetic field which is attributed to breaking of large droplets into smaller ones due to increase in instability at higher magnetic field.