HYPERFINE-STRUCTURE OF THE 3-P-3 STATE OF HE-3 AND ISOTOPE SHIFT FOR THE 2-S-3-3-P-3(0)-TRANSITION

The hyperfine structure of the He-3 1s 3p P-3 state and the He-3-He-4 isotope shift is determined by high precision measurements of the 1s 2s S-3(1) - 1s 3P P-3(J) transition frequencies near 389 nm. A direct frequency measurement is made without the need for wavelength calibration by tuning a single laser to the atomic frequency, and using a novel heterodyne method to observe beat frequencies with a stable reference laser. A fit to a theoretical model of hyperfine structure is used to determine the hyperfine shifts. Additional off-diagonal mixing effects are investigated to resolve a possible systematic discrepancy in the hyperfine intervals. The final isotope shift without hyperfine structure of 42184308+/-165 kHz is used to deduce an rms nuclear charge radius for He-3 of 1.956+/-0.042 fm. This is in good agreement with other values obtained from atomic isotope shift measurements, and a recent theoretical value of 1.958+/-0.006 fm. The present result helps to resolve substantial differences in the He-3 nuclear radius derived from electron-nuclear scattering measurements, and it provides a significant test of the nuclear three-body problem.