Spectroscopy and frequency measurement of the⁸⁷Sr clock transition by laser linewidth transfer using an optical frequency comb

We performed spectroscopic observations of the 698-nm clock transition in 87 Sr confined in an optical lattice using a laser linewidth transfer technique. A narrow-linewidth laser interrogating the clock transition was prepared by transferring the linewidth of a master laser (1064 nm) to that of a slave laser (698 nm) with a high-speed controllable fiber-based frequency comb. The Fourier-limited spectrum was then observed for an 80-ms interrogating pulse. We determined that the absolute frequency of the 5s 2 1 S 0 –5s5p 3 P 0 clock transition in 87 Sr is 429 228 004 229 872.0 (1.6) Hz referenced to the SI second.