Precision Measurement of the 2

Abstract
The 4f13 6s2 2F7/2–4f14 5d 2D5/2 3·43 μm infrared transition in 172Yb+ has been driven for the first time and measured to be 87 360 087(4) MHz. The frequency was determined by probing a cloud of 172Yb+ ions held in a radiofrequency trap in the presence of helium buffer gas. The infrared radiation was generated by difference frequency mixing in LiNbO3. The frequency measurement is part of a programme to locate the 4f14 6s 2S1/2–4f13 6s2 2F7/2 467 nm ultra-narrow transition in laser-cooled Yb+.