Energy Balance in a Laser-Induced Forward Transfer Process Studied by Shadowgraphy

Laser-induced forward transfer is a powerful technique for the patterned deposition of thin layers. Sensitive materials can be transferred using an intermediate sacrificial layer, which protects the material from direct laser irradiation. Among various materials, triazene polymers are very promising sacrificial layers, and therefore, their ablation behavior has a particular importance for the transfer. The ablation behavior of a single sacrificial layer of a specific triazene polymer was investigated using time-resolved shadowgraphy to understand and optimize the deposition process. We analyzed the evolution of the shock wave generated by the decomposition of the triazene polymer to estimate the thermodynamics of the process. The energy balance shows that a large part of the energy is released into the shock wave but that thermal and mechanical losses predominate. On the other hand, the kinetic energy of the flyer corresponds only to a few percent of the total energy. We also observed a difference in the shock wave energy between front side and back side ablation when a flyer of undecomposed triazene polymer is ejected. The presence of the flyer diminishes the shock wave energy by a factor of 2 in the most extreme case.