Precise measurements of UV atomic lines: Hyperfine structure and isotope shifts in the 398.8 nm line of Yb

– We demonstrate a technique for frequency measurements of UV transitions with sub-MHz precision. The frequency is measured using a ring-cavity resonator whose length is calibrated against a reference laser locked to the D2 line of Rb. We have used this to measure the 398.8 nm 1S0 ↔ P 1 line of atomic Yb. We report isotope shifts of all the seven stable isotopes, including the rarest isotope Yb. We have been able to resolve the overlapping Yb(F = 3/2) and Yb transitions for the first time. We also obtain highprecision measurements of excited-state hyperfine structure in the odd isotopes, Yb and Yb. The measurements resolve several discrepancies among earlier measurements. Precise measurements of the frequencies of atomic transitions are an important tool in expanding our knowledge of physics. For example, precise measurement of the D1 line in Cs [1] combined with an atom-interferometric measurement of the photon recoil shift [2] could lead to a more accurate determination of the fine-structure constant α. In addition, hyperfinestructure and isotope-shift measurements in atomic lines can help in fine-tuning the atomic wavefunction, particularly due to contributions from nuclear interactions. This is important when comparing theoretical calculations with experimental data in atomic studies of parity violation [3]. The most precise optical frequency measurements to date have been done using the recently developed frequency-comb method with mode-locked lasers [1], with errors below 100 kHz being reported. However, to the best of our knowledge, this technique has not yet been applied to UV spectroscopy, which relies on older and less-accurate techniques. In this Letter, we present the most comprehensive study of the 398.8 nm S0 ↔ P 1 line of atomic Yb. Yb (Z=70) is an attractive candidate for studying atomic parity violation [4] and the search for a permanent electric-dipole moment in atoms [5]. Laser-cooled Yb has also been proposed for frequency-standards applications [6]. The S0 ↔ P 1 line is widely used in laser-cooling experiments [5, 7]. Over the years, there has been much interest in this line, and its isotopic and hyperfine components have been measured using a variety of techniques – level-crossing and anti-crossing spectroscopy [8, 9, 10], Fabry-Perot cavity [11], saturatedabsorption spectroscopy [12], photon-burst spectroscopy [13], and most recently using optical (∗) E-mail: [email protected]