Intercombination line frequencies in $^{171}$Yb validated with the clock transition

Abstract

We have carried absolute frequency measurements of the (6s 2 ) 1 S 0 − (6s6p) 3 P 1 transition in 171 Yb (the intercombination line), where the spin-1/2 isotope yields two hyperfine lines. The measurements rely on sub-Doppler spectroscopy to yield a discriminator to which a 556 nm laser is locked. The frequency reference for the optical frequency measurements is a high-quality quartz oscillator steered to the GNSS timescale that is bridged with a frequency comb. The reference is validated to ∼ 3 × 10 −12 by spectroscopy on the 1 S 0 − 3 P 0 (clock) line in laser cooled and trapped 171 Yb atoms. From the hyperfine separation between the F = 1/2 and F = 3/2 levels of 3 P 1 we determine the hyperfine constant to be A( 3 P 1 ) = 3 957 833 (28) kHz.