Precision Laser Absorption Spectroscopy of Beryllium and Oxygen Atoms*

We share our most recent measurements of absolute transition frequencies of light elements. We use a titanium:sapphire laser locked to a Toptica Difference Frequency Comb in combination with a wavemeter to provide an absolute frequency reference. These measurements serve as the experimental component of the system of checks and balances between experiment and theory to advance our understanding of the finest details of quantum electrodynamics (QED).

In our measurements of the beryllium 2s^{2 1}S₀ → 2s 2p ¹P^o₁ transition, we use a large external magnetic field of approximately 400 gauss generated by a helmholtz coil to partially resolve the merged hyperfine structure and allow a determination of the absolute energy which is approximately 25 times more precise than the most recent experimental measurement[1] and approximately 150 times more precise than theoretical results[2]. We also report on progress in measuring the absolute transition frequency for the 2s 2p ³P^o_1,2,3 → 2s 4s ³S₁ transition.

In addition, with oxygen we have measured the absolute transition frequency of the three transitions connecting (⁴S^o) 3s ³S^o₁  → (⁴S^o) 3p ³P_0,1,2 and the nine transitions connecting  2s² 2p³ (⁴S^o) 3p ⁵P_1,2,3 →  2s² 2p³ (⁴S^o) 3d ⁵D^o_0,1,2,3,4 transitions. For the former, we also measured the isotope shift. In addition to providing guidance on future QED calculations, these measurements provide valuable information on nuclear structure to better understand quantum chromodynamics (QCD).