Precise Frequency Measurement of the 2$^{1}$S$_{0}$-3$^{1}$D$_{2}$ Two-Photon Transition in atomic $^{4}$He

TL;DR

This paper reports the first highly precise measurement of a specific two-photon transition in helium-4, significantly improving the accuracy over previous measurements and providing refined values for related atomic properties.

Contribution

The study achieves the first precise frequency measurement of the 2$^{1}$S$_{0}$-3$^{1}$D$_{2}$ transition in $^{4}$He using an optical frequency comb, enhancing measurement accuracy by a factor of 25.

Findings

Transition frequency measured as 594,414,291,803(13) kHz

Ionization energy of 2$^{1}$S$_{0}$ state determined as 960,332,040,866(24) kHz

Lamb shifts of 2$^{1}$S$_{0}$ and 2$^{3}$S$_{1}$ states improved by 1.6 times

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.