Investigation on the DC Stark shifts of strontium autoionization states for isotope-selective resonance ionization

Three-step resonance excitation to autoionization states is a promising isotope-selective ionization technique for atomic strontium (Sr). We measured for the first time the DC Stark shifts of ten Rydberg levels (n(eff) similar to 36 - 39, 50 - 55) of Sr-88 converging to the 4d D-2(3/2) limit using the 5s(2) S-1(0) -> 5s5p P-1(1)circle -> 5p(2) D-1(2) -> (4d D-2(3/2) Rydberg series) transition pathway. The polarizability aof each level was evaluated to be vertical bar alpha vertical bar similar to 10(-30) - 10(-28) [C-2.m(2).J(-1)] depending on the effective principal quantum number eta(eff), which indicates that the external electric field E in the ionization region should be of the order of 0.1 V/cm or less to suppress its effect on the observed spectra. Our experimental data on the DC Stark shift and polarizability of the Rydberg levels are useful for future isotope-selective detection of the radioisotope Sr-90 using three-step resonance excitation. (c) 2021 Elsevier Ltd. All rights reserved.