Optical selectivity calculations of ^90Sr isotope in double optical resonance photoionization schemes

Abstract

Seven new schemes have been theoretically studied using the density-matrix approach for the ns2(1S0)→nsnp(3P01 or 1P01)→nsms(1S0) and the ns2(1S0)→nsnp(3P01 or 1P01)→np2(1S0 or 1D2) double optical resonance photoionization pathways to establish the possibility of selective ionization of the rare strontium 90Sr isotope for continuous wave laser excitation. The double-resonance excitation is followed by photoionization using a 488 nm photon. Density-matrix equations for the double-resonance ionization have been numerically integrated by incorporating the effects of Doppler broadening, velocity-dependent interaction times, time varying Rabi frequencies, and laser bandwidths. All the optical selectivity calculations were carried out on a high-speed parallel processing machine. Theoretical computations on five previously studied photoionization pathways have also been performed and tabulated for the sake of completeness. The conditions for obtaining optimum optical selectivities have been evaluated. This study results in seven new photoionization pathways. The optical selectivities are a few orders higher compared to the previously studied photoionization schemes for five out of the seven schemes studied. The remaining two schemes are slightly better than the previously studied schemes.