Investigation of isotope shifts and Stark shifts in the strontium Rydberg state via 5s21S0→5s5p1P10→5p1/25p1/2→4d3/2nljn∗=39.4

Abstract

Resonance Ionization Spectrometry (RIS) is a highly sensitive analytical technique that utilizes differences in atomic structure between isotopes to achieve isotope selectivity. In recent years, multi-step resonance transitions have been developed to excite target isotopes from the ground state to high Rydberg states, simultaneously enhancing isotope selectivity and ionization efficiency, thereby improving the overall detection sensitivity of RIS. This study investigates a three-step RIS scheme $(5s^{21}{S}_0\to 5s5p^1{P}_1^0\to 5p_{1/2}5p_{1/2}\to 4d_{3/2}{\mathrm{nl}}_j\left(n^{\ast }=39.4\right)$) for Sr isotope analysis, the isotope shifts of natural Sr isotopes were measured in the first and second transitions ($5s^{21}{S}_0\to 5s5p^1{P}_1^0\to 5p_{1/2}5p_{1/2}$), and the isotope shift for Sr-90 relative to Sr-88 was estimated. Additionally, Stark shifts of Sr-88 atoms in the Rydberg state under various external electric field conditions were precisely measured using a pulsed electric field. The results revealed that the external static electric fields caused energy level shifts for Sr-88 Rydberg atoms, with opposite directions. Furthermore, as the field strength increased, a transition from quadratic to linear Stark shifts was observed. These findings provide theoretical support for improving spectral resolution and transition selectivity in RIS methods involving Rydberg states. The detailed analysis of Rydberg state behavior under electric fields also offers valuable data for evaluating and compensating for field-induced perturbations in final energy level transitions, and serves as a reference for applying RIS to other elements or systems in similar Rydberg states for complex analyses.