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.