A computational study of femtosecond laser sintering of copper nanoparticles

Femtosecond Selective Laser Sintering (fs-SLS) has much advantage of finer resolution of 3D printing as the Heat Affected Zone (HAZ) of the irradiated samples is much narrower comparing to other laser sources. Recent studies report that fs- SLS technique suffers from ablation problem. The ultrafast nature of femtosecond laser causes different ablation mechanism that are not observed in nanosecond and continuous wave lasers. The theoretical understanding of the femtosecond laser ablation mechanisms of MNPs is the first step to develop a novel technique of fs-SLS. In this study, we develop a Two Temperature based ablation model considering two possible mechanisms; Thermal stress and Coulomb Explosion. We conduct simulation studies in different sizes of MNPs (10 nm, 100 nm and 1 μm) and investigate which ablation mechanism is dominant over the other in different particle sizes. Under high sintering fluences, 10 nm particles is both vulnerable to the thermal stress and Coulomb explosion while thermal stress is the dominant ablation mechanism in 100 nm and 1 μm. However, in lower fluence, the Coulomb Explosion is the dominant in 10 nm MNPs. We also found that there is a limit of ablation depth with Coulomb Explosion. After that, we conduct the double pulse sintering (DPS) simulation in 100 nm MNPs, and it shows that a significant reduction of thermal stress can be observed while there is no sign of suppression of Coulomb Explosion. We suggest that DPS could be the effective fs-SLS technique for the better sintering of MNPs