1557 nm处的氦2 3S - 2 1 S计量
Helium 2 3S - 2 1S metrology at 1557 nm
摘要：
提出了在亚稳态氦原子准直慢原子束中激发1557 nm处1 s2 s3 S1 - 1 s2 s1 S 0磁偶极（M1）“禁戒”跃迁的实验方案。结果表明，用2 W窄带通信光纤激光器的光束与原子束垂直相交，可以实现5000 /s的激发速率。多普勒限制的亚MHz光谱线宽的预期。在一维光晶格几何结构中，用2 W激光进行俘获和光谱分析，可以实现2%的俘获和冷却原子的无多普勒激发。这种跃迁的非常小的自然线宽（8 Hz）为氦原子的原子结构计算的精确测试提供了机会。3 He-4 He同位素位移的测量允许精确确定两种同位素的核电荷半径的差异。
英文摘要：
An experiment is proposed to excite the 'forbidden' 1s2s 3S1 - 1s2s 1S0 magnetic dipole (M1) transition at 1557 nm in a collimated and slow atomic beam of metastable helium atoms. It is demonstrated that an excitation rate of 5000 /s can be realised with the beam of a 2W narrowband telecom fiber laser intersecting the atomic beam perpendicularly. A Doppler-limited sub-MHz spectroscopic linewidth is anticipated. Doppler-free excitation of 2% of trapped and cooled atoms may be realised in a one-dimensional optical lattice geometry, using the 2W laser both for trapping and spectroscopy. The very small (8 Hz) natural linewidth of this transition presents an opportunity for accurate tests of atomic structure calculations of the helium atom. A measurement of the 3He - 4He isotope shift allows for accurate determination of the difference in nuclear charge radius of both isotopes.
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