Institute of Photonics Technologies, National Tsing Hua University, Hsinchu 30013, Taiwan.
Phys Rev Lett. 2013 Jul 5;111(1):013002. doi: 10.1103/PhysRevLett.111.013002. Epub 2013 Jul 1.
We report a precision frequency measurement of the (4)He 2(1)S(0)→2(1)P(1) transition at 2058 nm. The saturated absorption spectroscopy is performed in a rf discharge sealed-off cell with a volume Bragg grating-based Tm:Ho:YLF laser. The absolute transition frequency measured using a fiber optical frequency comb is 145 622 892 822 (183) kHz with a relative uncertainty of 1.3×10(-9). Our result is ten times more precise than current best theoretical calculations and is in reasonable agreement with the calculated values. However, the ionization energy of the 2(1)P(1) state, derived from our result and other precisely measured transitions, shows a discrepancy of approximately 3.5σ with the most precise atomic theory. We have also determined the isotope shift between (3)He and (4)He to be 4248.7 (5.3) MHz, which is more precise than the previous measurement by one order of magnitude.
我们报告了在 2058nm 处对 (4)He 2(1)S(0)→2(1)P(1) 跃迁的精密频率测量。该饱和吸收光谱是在一个带有基于体积布拉格光栅的 Tm:Ho:YLF 激光的射频放电密封单元中进行的。使用光纤光频梳测量的绝对跃迁频率为 145622892822(183)kHz，相对不确定度为 1.3×10(-9)。我们的结果比当前最精确的理论计算精确十倍，与计算值吻合良好。然而，从我们的结果和其他精确测量的跃迁中得出的 2(1)P(1)态的电离能与最精确的原子理论存在约 3.5σ 的差异。我们还确定了 (3)He 和 (4)He 之间的同位素位移为 4248.7(5.3)MHz，比以前的测量精度提高了一个数量级。
