Thermalization of a UV laser ablation plume in a background gas: From a directed to a diffusionlike flow.

Combined diagnostic measurements of deposition rates and ion time-of-flight signals have been employed to study the expansion of a laser ablation plume into a background gas. With increasing gas pressure the angular distribution of the collected ablated atoms becomes broader, while the total collected yield decreases. The total collected yield shows three separate regimes with increasing pressure, a vacuumlike regime, a transition regime with increasing plume broadening and splitting of the ion signal, and at the highest pressure a diffusionlike regime with a broad angular distribution. In the high-pressure regime the expansion can be described by a simple model based on diffusion from a confined plume.