Modelling of multistage selective photoionisation in a three-dimensional cavity

An analysis is made of physical models of selective three-stage photoionisation of a vapour in a three-dimensional cavity. These models have been used in theoretical analyses of preparation of significant amounts of highly enriched ¹⁶⁸Yb by the AVLIS (atomic-vapour laser isotope separation) method. A comparison of the model predictions with experiments shows that a three-dimensional model ignoring the absorption of laser radiation in a medium describes well the experimental results obtained for the second and third ionisation stages. The first excitation stage is described satisfactorily by a model in which absorption is included. A comparison of the calculated and experimental results is used to find the coefficient (65%) representing ion extraction from a laser plasma.