Emission induced by collision of two plumes during pulsed laser ablation

We observed plume expansion dynamics during pulsed laser ablation when two plumes collided head-on. Si and Ge targets were placed parallel each other, and they were irradiated simultaneously by two pulsed lasers. A new emission appeared near the center of the targets from 250 ns after the irradiation. However, the predominant ejected species is neutral SiI or GeI at this time region when an individual single target is irradiated, and the new emission emerged by collision is a mixture of ionized SiII and GeII. This indicates that the kinetic energy of the collision excites the species to an ionized state. The intensity of this new emission decreased by increasing the background gas pressure. This suggests that collision between two plumes induces a higher-temperature plasma. Since the new emission is composed of ionized Si and Ge species and remains a relatively long period after the collision, this technique will provide a new reactive field to prepare a new kind of alloy nanomaterials.