Spectroscopy of a narrow-line optical pumping transition in dysprosium

We present measurements of the hyperfine coefficients and isotope shifts of the Dy I $683.731 $nm transition, using saturated absorption spectroscopy on an atomic beam. A King Plot is drawn resulting in an updated value for the specific mass shift $\delta \nu_\mathrm{684,sms}^\mathrm{164-162}=-534 \pm 17 MHz$. Using fluorescence spectroscopy we measure the excited state lifetime $\tau_{684}=1.68(5) \mu$s, yielding a linewidth of $\gamma_\mathrm{684} = 95 \pm 3 kHz$. We give an upper limit to the branching ratio between the two decay channels from the excited state showing that this transition is useable for optical pumping into a dark state and demagnetization cooling.