Optogalvanic spectroscopy of metastable states in Yb⁺

Abstract

The metastable ²F_7/2 and ²D_3/2 states of Yb⁺ are of interest for applications in metrology and quantum information and also act as dark states in laser cooling. These metastable states are commonly repumped to the ground state via the 638.6 nm ²F_7/2–¹D[5/2]_5/2 and 935.2 nm ²D_3/2–³D[3/2]_1/2 transitions. We have performed optogalvanic spectroscopy of these transitions in Yb⁺ ions generated in a discharge. We measure the pressure broadening coefficient for the 638.6 nm transition to be 70±10 MHz mbar⁻¹. We place an upper bound of 375 MHz/nucleon on the 638.6 nm isotope splitting and show that our observations are consistent with theory for the hyperfine splitting. Our measurements of the 935.2 nm transition extend those made by Sugiyama et al., showing well-resolved isotope and hyperfine splitting (Sugiyama and Yoda in IEEE Trans. Instrum. Meas. 44: 140, 1995). We obtain high signal-to-noise, sufficient for laser stabilisation applications (Streed et al. in Appl. Phys. Lett. 93: 071103, 2008).