SELECTIVE PHOTOIONIZATION OF YB-168 IN AN EXTENDED OPTICALLY DENSE MEDIUM

Mathematical simulation methods are used to optimise three-stage isoto pically selective photoionisation of atoms of the ytterbium-168 isotop e. The influence of nonlinear deformation of laser beams is taken into account. It is shown that exact tuning of the laser radiation frequen cies to the frequencies of the lines of radiative transitions in the y tterbium-168 atom results in absorption of the laser radiation by atom s of other isotopes and in self-focusing of the laser beams. Introduct ion of a two-photon detuning reduces considerably the influence of the absorption and self-focusing. A determination is reported of the two- photon detuning, and of the dimensions and the spatial distribution of the power in the laser beam required to ensure that the absorption an d nonlinear self-focusing of laser beams do not reduce significantly t he ionisation efficiency.