High-precision spectroscopy using the ion-trapping technique

This paper reports on the use of laser-microwave double-resonance spectroscopy to study trapped 113Cd+ ions in the presence of helium buffer gas, and gives the results of laser cooling experiments on the trapped ions. The effectiveness of using a combination of ion-trapping with laser cooling to separate isotopes is assessed. Using spectroscopy to examine buffer-gas-cooled ions, the ground-state hyperfine splitting of trapped 113Cd+ ions was recorded at 15 199 862 858(2) Hz. In order to improve this measurement, laser cooling of trapped ions was carried out using a linear Paul trap. When laser cooling 113Cd+ ions, the microwave transition between the ground-state hyperfine structures was used to repump ions. Occurance of a phase transition from cloud-state to crystal-state of trapped ions was confirmed by observing both spectra and images of fluorescing ions. The results obtained may be useful when a microwave frequency standard based on Cd+ ions is established.