Abstract Femtosecond (fs) laser has emerged as an effective technique for nanojoining. However, the role of nanowire diameter and the associated electric field distribution under fs laser irradiation in nanojoint formation and polycrystalline evolution remains unclear. In this study, AgNW nanojoints were fabricated via fs laser irradiation, and the electric field intensity distribution was simulated using the three-dimensional finite-difference time-domain (FDTD) method.