Abstract

Doppler-free spectroscopy has been performed on thorium and protactinium isotopes to gain a detailed understanding of the underlying physics of spectral features. Characterizing phenomena such as Lamb dips and optical pumping are important in understanding and optimizing resonance ionization mass spectrometry (RIMS) analysis. Measurement of these isotopes by RIMS is used in U-series disequilibrium dating of geological samples of the last 400,000 years. Isotope shifts and hyperfine structure of ²³²Th, ²³⁰Th, ²²⁹Th, ²³³Pa, and ²³¹Pa are reported for several transitions. The Doppler-free spectra of Th showed an interesting effect, which was strongly dependent on laser power, in which a narrow peak replaced the usual Lamb dip. These results and a detailed analysis will be presented and discussed.

© 1992 Optical Society of America