Heat transfer analysis of nanosecond laser-induced forward transfer

Laser-induced forward transfer (LIFT) uses nanosecond laser pulses to remove and transfer material for localized deposition. An experimental study was carried out to determine the optimum conditions for LIFT and to evaluate this technique for different materials. Numerical simulations were performed to better understand the heat transfer processes that initiate laser induced forward transfer.; Laser-induced forward transfer was used to deposit aluminum and nickel features onto a glass substrate using a Q-switched Neodymium-doped Yttrium Aluminum Garnet (Nd:YAG) laser with a pulse width of 14 nanoseconds. The influence of the metal film thickness and laser fluence were evaluated by scanning electron microscopy of the metal film and the deposited material. Three transfer regimes were observed for increasing fluences values. The first regime, at low laser fluence, produced structures such as individual droplets or ring-like elements similar in size or smaller to the laser spot size. The second regime, when the laser fluence is above a threshold value, is characterized by localized material transfer near the center of the laser spot. Further increasing the fluence resulted in spatter of the material outside of the laser spot which represents the third regime.; A numerical study of LIFT was conducted to determine the temperature distribution, melt zone, and free surface deformation resulting from laser irradiation. The initial numerical analysis used a pure conduction model with phase change capability. An improved model was developed to permit the motion of the metal once in the molten phase and to account for the temperature dependency of the material properties. The addition of the motion in the simulation produced deformations of the metal film, similar to that observed in experiments. The numerical simulations performed using this model confirmed that the deformation of the metal is produced by its volumetric expansion and provided the evolution of the moving solid-liquid front and metal-air interface during laser thin film heating.