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Absolute frequency measurements of the $D_2$ line and fine-structure interval in $^{39}$K

Ayan Banerjee·Vasant Natarajan
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Abstract

We report a value for the $D_2$-line frequency of $^{39}$K with 0.25 ppb uncertainty. The frequency is measured using an evacuated ring-cavity resonator whose length is calibrated against a reference laser. The $D_2$ line presents a problem in identifying the line center because the closely-spaced energy levels of the excited state are not resolved. We use computer modelling of the measured spectrum to extract the line center and obtain a value of 391 015 578.040(75) MHz. In conjunction with our previous measurement of the $D_1$ line, we determine the fine-structure interval in the $4P$ state to be 1 729 997.132(90) MHz. The results represent significant improvement over previous values.

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Ayan Banerjee, Vasant Natarajan. 2004-01-30. Absolute frequency measurements of the $D_2$ line and fine-structure interval in $^{39}$K. https://doi.org/10.1103/physreva.70.052505

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