摘要
We have measured the absolute frequency of the 2S01-3D21 two-photon transitions in He3 at 1009 nm based on a cesium frequency standard through an optical frequency comb. The measured frequencies are 594 384 961.072(19) MHz for the 2S0,1/21-3D2,5/21 transition and 594 384 821.209(15) MHz for the 2S0,1/21-3D2,3/21 transition with relative uncertainties of 2.5×10-11 and 3.9×10-11, respectively. The determination of the 2S01-3D21 two-photon transition frequency, without hyperfine effect, in He3 is 594 384 761.556(12) MHz. The deduced isotope shift between He3 and He4 is 29.530246(18) GHz. The difference of the squares of the nuclear charge radii is deduced to be 1.059(25)fm2. Finally, by combining other precise measured transitions, we are able to derive the 3D13-3D21 separation in He3 to be 101 058 203(56) kHz, which is an improvement by a factor of 89 compared to previous work.