Precision frequency measurements of He3,4 2P3→3D3 transitions at 588 nm

Abstract

We report the frequency measurements of the $2\phantom{\rule{0.16em}{0ex}}^{3}P\ensuremath{\rightarrow}3\phantom{\rule{0.16em}{0ex}}^{3}D$ transitions in $^{3,4}\mathrm{He}$ at 588 nm using an optical frequency comb stabilized laser system. The Doppler-free spectra of the $2\phantom{\rule{0.16em}{0ex}}^{3}P\ensuremath{\rightarrow}3\phantom{\rule{0.16em}{0ex}}^{3}D$ transitions are demonstrated in an rf discharged sealed-off helium cell using intermodulated fluorescence spectroscopy. The measured absolute frequency of the $^{4}\mathrm{He}\phantom{\rule{4pt}{0ex}}2\phantom{\rule{0.16em}{0ex}}{^{3}P}_{0}\ensuremath{\rightarrow}3\phantom{\rule{0.16em}{0ex}}{^{3}D}_{1}$ transition is 510 059 755.352(28) MHz, which is more precise than the previous measurement by two orders of magnitude. The ionization energies of the $^{4}\mathrm{He}\phantom{\rule{4pt}{0ex}}2\phantom{\rule{0.16em}{0ex}}{^{3}P}_{0}$ and $2\phantom{\rule{0.16em}{0ex}}{^{3}S}_{1}$ states can be derived from our result and agree very well with the previous experimental values. More importantly, the Lamb shift of the $2\phantom{\rule{0.16em}{0ex}}{^{3}S}_{1}$ state can be deduced to be 4057.086(34) MHz, which is two times more precise than the previous result. In addition, the absolute frequencies of the $2\phantom{\rule{0.16em}{0ex}}{^{3}P}_{0,1/2}\ensuremath{\rightarrow}3\phantom{\rule{0.16em}{0ex}}{^{3}D}_{1,3/2}, 2\phantom{\rule{0.16em}{0ex}}{^{3}P}_{0,1/2}\ensuremath{\rightarrow}3\phantom{\rule{0.16em}{0ex}}{^{3}D}_{1,1/2}$, and $2\phantom{\rule{0.16em}{0ex}}{^{3}P}_{0,1/2}\ensuremath{\rightarrow}3\phantom{\rule{0.16em}{0ex}}{^{3}D}_{2,3/2}$ transitions in $^{3}\mathrm{He}$ are measured. Our precision surpasses the theoretical calculations by more than one to two orders of magnitude. The hyperfine separations of the $3\phantom{\rule{0.16em}{0ex}}^{3}D$ states in $^{3}\mathrm{He}$ and the frequency differences between $^{4}\mathrm{He}$ and $^{3}\mathrm{He}$ transitions are also presented.