Intermittent optical frequency measurements to reduce the dead time uncertainty of frequency link

The absolute frequency of the ⁸⁷ Sr lattice clock transition was evaluated with an uncertainty of 1.1× 10⁻¹⁵ using a frequency link to the international atomic time (TAI). The frequency uncertainty of a hydrogen maser used as a transfer oscillator was reduced by homogeneously distributed intermittent measurement over a five-day grid of TAI. Three sets of four or five days measurements as well as systematic uncertainty of the clock at 8.6× 10⁻¹⁷ have resulted in an absolute frequency of ⁸⁷ Sr\ ¹S₀ - ³P₀ clock transition to be 429 228 004 229 872.85 (47) Hz.