Numerical studies of isotopic selective photoionization of ytterbium in a three-step ionization scheme

Selective photoionization of ytterbium isotope is studied numerically based on a three-step photoionization scheme, 4f ¹⁴6s ^{2 1}S ₀ (0 cm ⁻¹) → 4f ¹⁴6s6p ³P ₁ (17992.008 cm ⁻¹) → (4f ¹³6s ²6p) (7/2, 3/2) ₂ (35196.98 cm ⁻¹) → auto-ionization state (52353 cm ⁻¹) → Yb ⁺, by the density matrix theory with the consideration of atomic hyperfine structures and magnetic sublevels. To examine the physical model, the numerical isotopic abundance of ytterbium is compared with that from mass spectroscopy experiment, showing that they are in good agreement with each other. The excitation process and ionization process of ytterbium, especially for odd isotopes, are discussed and analyzed in detail on this basis. The effects of frequency detuning, power densities, spectral bandwidths, polarization of two excitation lasers, and atomic Doppler broadening on the total ionization yield and isotopic abundance are investigated numerically and the optimal excitation conditions for ¹⁷⁶Yb enrichment are identified semi-quantitatively.