Precise Frequency Measurement of the 2${}^1$S${}_0$-3${}^1$D${}_2$ Two-Photon Transition in atomic ${}^4$He

Abstract

We present the first precise frequency measurement of the 2${}^1$S${}_0$-3${}^1$D${}_2$ two-photon transition in ${}^4$He at 1009 nm. The laser source at 1009 nm is stabilized on an optical frequency comb to perform the absolute frequency measurement. The absolute frequency of 2${}^1$S${}_0$-3${}^1$D${}_2$ transition is experimentally determined to be 594 414 291 803(13) kHz with a relative uncertainty of 1.6 $\times$ 10${}^{-11}$ which is more precise than previous determination by a factor of 25. Combined with the theoretical ionization energy of the 3${}^1$D${}_2$ state, the ionization energy of the 2${}^1$S${}_0$ state is determined to be 960 332 040 866(24) kHz. In addition, the deduced 2${}^1$S${}_0$ and 2${}^3$S${}_1$ Lamb shifts are 2806.817(24) and 4058.8(24) MHz respectively which are 1.6 times better than previous determinations.

5 pages, 6 figures