Narrow-line diode laser system for laser cooling of strontium atoms on the intercombination transition

We report a diode laser system developed for narrow-line cooling and trapping on the S-1(0)-P-3(1) intercombination transition of neutral strontium atoms. Doppler cooling on this spin-forbidden transition with a line width of Gamma/2pi=7.1 kHz enables us to achieve sub-muK temperatures in a two-step cooling process. The required reduction of the laser line width to the kHz level was achieved by locking the laser to a tunable Fabry-Perot cavity. The long-term drift (>0.1 s) of the reference cavity was compensated by employing the saturated absorption signal obtained from Sr vapor in a heat pipe of novel design. We demonstrate the potential of the system by performing spectroscopy of Sr atoms confined to the Lamb-Dicke regime in a one-dimensional optical lattice.