Numerical studies on lutetium isotopic selective photoionization based on a three-step ionization scheme.

Numerical studies of lutetium selective photoionization have been carried out based on a three-step photoionization scheme, 5d6sD → 5d6s6pF → 5d6s7sD → (53,375 cm) → Lu, by the density matrix theory. Atomic hyperfine structures and magnetic sublevels are considered in our photoionization dynamics model. To examine the effectiveness of this model, the simulated Lu ion strengths are compared with the experimental results, and the simulated excitation cross sections of Lu excitation channels are compared with the analytical and experimental results. Semi-quantitative agreements are acquired for these two cases. On this basis, selective photoionization processes of two lutetium isotopes are simulated and discussed. Considering the ionization probability and abundance of target isotope, the 8.5-9.5-8.5 two-step excitation channel is optimal for Lu enrichment from natural lutetium. The influences of laser parameters and atomic Doppler broadening are presented numerically and optimization excitation conditions are identified. For the co-propagating excitation lasers, extra-narrow laser bandwidth (at the magnitude of 0.1 GHz) and atomic Doppler broadening (smaller than 0.3 GHz) is required. A new time-delayed configuration is proposed to implement multiple counter-propagating laser exposures for high target isotope abundance at the larger atomic Doppler broadening.