Selective resonance ionization of calcium odd isotopes with odd–even selection rules

Overview

This study demonstrates selective resonance ionization of calcium isotopes through application of angular momentum selection rules in a three-step laser ionization scheme. The work employs linearly polarized light in a J=0-1-0 transition configuration to achieve isotope-specific excitation, enabling suppression of the abundant Ca-40 isotope while selectively ionizing rare odd isotopes, particularly Ca-43 and Ca-41.

Methods and approach

Resonance ionization spectroscopy was conducted using a three-step laser excitation scheme (J=0-1-0) with linearly polarized light to exploit electric dipole selection rules for angular momentum coupling. Isotope selectivity was controlled through systematic variation of linear polarization angle using a half-waveplate retarder. Orthogonal transition polarizations were applied to suppress even-isotope excitation while permitting odd-isotope pathways. Spectroscopic measurements were extended to Rydberg-level transitions to assess selectivity throughout the ionization cascade.

Key Findings

Angular momentum selection rules successfully suppressed Ca-40 ionization while enabling Ca-43 excitation as a function of linear polarization orientation. Rydberg-level spectroscopy confirmed sustained selectivity in the resonance ionization process. Maximum selectivity, dependent on hyperfine transition resolution, reached a separation coefficient of β=9×10³, demonstrating significant isotopic discrimination.

Implications

The demonstrated method provides a relatively straightforward approach to enhancing isotopic selectivity in resonance ionization by leveraging polarization-controlled angular momentum constraints. The technique requires minimal optical complexity, utilizing a simple half-waveplate for polarization control. Application to isolation of rare calcium isotopes addresses requirements in multiple research domains, including quantum information processing via trapped-ion systems with Ca-43 and investigations in cosmology and biomedical science employing Ca-41 as a tracer isotope.