Atomic-scale mechanisms of femtosecond laser double-pulse sintering in Cu nanoparticles: A multiscale simulation study

Femtosecond laser sintering offers a promising route for fabricating Cu-based micro- and nano-devices, yet optimizing processing conditions to balance sintering efficiency with minimal thermal damage remains challenging. In this study, a comprehensive multi-scale investigation of dual-pulse femtosecond laser sintering of Cu nanoparticles is presented using a combined molecular dynamics and two-temperature model (MD-TTM) simulation framework. Initially, the nanoscale melting point was determined under both slow and rapid heating conditions, revealing a reduction compared to bulk copper due to size effects. Subsequent simulations explored the effects of inter-pulse delay and energy distribution on electron–lattice energy coupling and sintering kinetics. Our results indicate that, within a critical delay threshold (approximately 30 ps), dual-pulse processing can synergistically regulate electron temperature, suppress thermionic emission, and accelerate neck formation. Furthermore, by comparing different energy injection schemes, we found that while a high-low energy combination improves processing speed, an equal energy ratio yields the best overall balance between electron temperature control and morphological evolution. These findings provide theoretical guidance for tailoring dual-pulse laser parameters, offering enhanced process controllability and improved material quality for advanced laser sintering applications.