Interrogation Laser for a Strontium Lattice Clock

We report on the setup and characterization of a 698-nm master–slave diode laser system to probe the $^{1}\hbox{S}_{0} {-}^{3} \hbox{P}_{0}$ clock transition of strontium atoms confined in a 1-D optical lattice. A linewidth on the order of about 100 Hz of the laser system has been measured with respect to an ultrastable 657-nm diode laser with 1-Hz linewidth using a femtosecond fiber comb as a transfer oscillator. The laser has been used to measure the magnetically induced $^{1}\hbox{S}_{0} {-}^{3} \hbox{P}_{0}$ clock transition in $^{88}\hbox{Sr}$, where a linewidth of 165 Hz has been observed. The transfer oscillator method provides a virtual beat signal between the two diode lasers that has been used to phase lock the 698-nm laser to the 1-Hz-linewidth laser at 657 nm, transferring its stability to the 698-nm laser system.