甲醇中光学衍生的射频基准：用于基础物理学天体物理测试的亚千赫兹参考
Optically Derived Radio-Frequency Benchmark in Methanol: A Sub-kHz Reference for Astrophysical Tests of Fundamental Physics
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中文总结 AI 辅助
研究通过测量甲醇近红外振转跃迁确定其12.2GHz跃迁频率，利用波长调制NICE - OHMS和光学频率梳等技术，实现高精度测量，得到亚千赫兹基准，证明光学三角测量可用于有内旋转的非手性分子。
中文摘要 AI 辅助
在太空中观测到的甲醇无线电线可灵敏探测质子与电子质量比在宇宙时间里是否变化，但此类测试需要高精度实验室静止频率。本文通过测量近红外振转跃迁而非直接测量微波谱线，确定了天体物理学中重要的甲醇12.2GHz 3₋₁E -- 2₀E跃迁频率。利用锁定在超稳定光学频率梳上的波长调制NICE - OHMS，并通过光纤链路参考氢脉泽频率标准，测量了1.4μm（216THz）附近的兰姆凹陷频率，统计重复性为10Hz，绝对不确定度低至130Hz。共享共同高能级的光学跃迁对形成三角测量方案以得出基态转动组合差。得到12178596.415(135)kHz，比早期分子束微波光谱法精度提高20倍，与最近的自由感应衰减测量结果一致。该结果为关键的射电天文甲醇谱线建立了亚千赫兹实验室基准，并证明光学三角测量可扩展到具有内旋转的非手性分子。
英文摘要
Methanol radio lines observed in space provide sensitive probes of whether the proton-to-electron mass ratio has changed over cosmic time, but such tests require laboratory rest frequencies with very high accuracy. Here we determine the frequency of the astrophysically important 12.2 GHz $3_{-1}$E -- $2_{0}$E transition of CH$_3$OH by measuring near-infrared rovibrational transitions rather than the microwave line directly. Using wavelength-modulated NICE-OHMS locked to an ultra-stable optical frequency comb and referenced via a fiber link to a hydrogen-maser frequency standard, we measure Lamb-dip frequencies near 1.4 $μ$m (216 THz) with 10 Hz statistical reproducibility and absolute uncertainties as low as 130 Hz. Pairs of optical transitions sharing common upper levels form a triangulation scheme that yields the ground-state rotational combination difference. We obtain 12 178 596.415(135) kHz, improving on earlier molecular-beam microwave spectroscopy by a factor of 20 and agreeing with a recent free-induction-decay measurement. This result establishes a sub-kHz laboratory benchmark for a key radio-astronomical methanol line and demonstrates that optical triangulation can be extended to non-chiral molecules with internal rotation.
