Study on ejection mechanism of copper film induced by nanosecond laser

Laser induced ejection mechanism of micron thick copper film was studied using nanosecond Nd:YAG laser pulses. By carrying out the experiments with different energy of laser pulses 10-500 J, three different ejection regimes were revealed:no ejection, stable ejection and sputtering. In the stable ejection regime, the forward and backward ejection were found to be simultaneously induced by a single laser shot. This phenomenon opened a way to the fabrication of microstructures on both the receiving and the donor substrate. The temperature field and the phase transition in the copper film were analyzed using the finite element method, which revealed that the laser-induced ejection was mainly caused by the hydrodynamics behavior of the molten and the evaporated material. The laser energy thresholds for stable ejection were characterized based on the thermodynamics calculations. The laser induced hydrodynamics behavior (bubble dynamics) was well described by the Rayleigh-Plesset equation, and which was solved numerically in the paper. It was discovered that rapid bubble expansion and collapse were the main causes of the forward and backward ejections, respectively. Based on the experimental and numerical findings, the controlling schemes of the laser pulse parameters for the stable ejections were introduced.