Intercombination line frequencies in ¹⁷¹Yb validated with the clock transition

Abstract

We have carried absolute frequency measurements of the (6s2)1S0−(6s6p)3P1 transition in 171Yb (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 time scale that is bridged with a frequency comb. The reference is validated to ∼3×10−12 by spectroscopy on the 1S0−3P0 (clock) line in laser cooled and trapped 171Yb atoms. From the hyperfine separation between the F=1/2 and F=3/2 levels of 3P1, we determine the hyperfine constant to be A(3P1)=3957833(28)kHz.