Dynamics of colliding laser ablation plumes in background gas

We observed plume expansion dynamics during pulsed laser ablation in background gas when two plumes collided head-on. The Si target is irradiated followed by the Ge target with delay time td. When td is larger than a few μs, the Si plume emission quenches before the irradiation of the Ge target. Re-emission of quenched Si atomic species by the collision with counter Ge plume is observed. The intensity and lifetime of Si re-emission decrease with increasing td, and rapid decrease at around td = 60 μs is observed. These results indicate that non-luminescent Si atomic species exist between targets up to about td = 60 μs and effects of the collision rapidly decrease at above about td = 60 μs. Effects of the collision of Si and Ge plumes and the re-emission of quenched Si atomic species are discussed.