Absolute Frequency Measurements of the D Lines in 9Be+ Using a Single Trapped Ion
Optical frequencies of the D line transitions in 9Be+ were measured with a relative uncertainty of Δν/ν=5×10−11. The results represent the highest accuracy achieved on a broad electric dipole-allowed (E1) transition in a trapped ion experiment to date, enabled in part by detailed consideration of photon recoil and quantum interference. Measurements were made on a single laser-cooled ion stored in a radio frequency Paul trap, using a spectroscopy laser stabilized to an optical frequency comb and referenced to UTC (NIST). The uncertainties in the D1 and D2 lines have been reduced by a factor of 10 and 30, respectively, compared to previous work. We have extracted the 2P fine structure splitting, Δνfs=197 064.54(7) MHz, and the 2P1/2 hyperfine constant, AP1/2=−117.92(4) MHz.