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

We present precise frequency measurement of the 2 S-1(0)-3(1)D(2) two-photon transition in He-4 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 S-1(0)-3(1)D(2) transition is experimentally determined to be 594 414 291.803(13) MHz with a relative uncertainty of 1.6 x 10(-11), which is more precise than previous determinations by a factor of 25. In combination with the theoretical ionization energy of the 3 D-1(2) state, the ionization energy of the 2 S-1(0) state is determined to be 960 332 040.823(24) MHz. In addition, the deduced 2 S-1(0) and 2 S-3(1) Lamb shifts are 2806.864(24) MHz and 4058.130(24) MHz, respectively, which are 1.6 times better than previous determinations, and the fine structure 3 D-3(1)-3(1)D(2) is determined to be 101 143.889(29) MHz, improving the precedent determination by a factor of 11.