Multiple-scattering effects in laser ablation plume propagation in gases

Langmuir probe technique has been employed to characterize the dynamics of UV laser ablation plasma ions from a silver target in different background gases (He, Ne, Ar and Xe). For all these gases the ion time-of-flight signals show progressive formation of a slower component as the gas pressure is increased. In the case of heavier gases (Ar and Xe) this slower component is clearly resolved from the vacuum peak ( plume splitting ), as has been previously reported. The pressure variation of the collected ion yield deviates markedly from a simple exponential decay, and a new approach, based on multiple-elastic-scattering processes, has been developed to describe these results as well as to provide elastic collision cross-sections which were previously not available. For the heavier gases, it has been possible to analyze the two ion components separately, and to estimate both the elastic collision cross-sections and the scattering order for the different gases.