Isotope shift and hyperfine structure measurements on triple resonance excitation to the autoionizing Rydberg state of atomic strontium

Abstract

Triple resonance excitation to the autoionizing Rydberg state of atomic strontium was studied for the isotope-selective photoionization of strontium-90 (90Sr). We investigated a new resonance ionization scheme, namely, 689.4 nm–472.4 nm–404.2 nm that is less affected by the multiphoton ionization induced by the first (689.4 nm) laser compared to the scheme in our previous study, namely, 689.4 nm–487.4 nm–393.8 nm. The isotope shifts and hyperfine structure constants of stable Sr isotopes were measured for the second and third transitions of these two schemes. Thus, the 90Sr isotope shift for each of the four transitions was evaluated using the King plot analysis. Under the current laser conditions, no significant difference was observed in the measured 90Sr optical isotopic selectivity between these two schemes, but the new scheme could show better selectivity if the first (689.4 nm) laser output is increased to improve the ionization efficiency. Our spectroscopic data will be useful for future analysis of 90Sr in real samples and may also help promote studies in other fields, such as precision measurements using cold atoms in optical traps.