Spectroscopy of a narrow-line optical pumping transition in atomic 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 δν(684,sms)(164-162)=-534±17 MHz. Using fluorescence spectroscopy, we measure the excited state lifetime τ684=1.68(5) μs, yielding a linewidth of γ684=95±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 usable for optical pumping into a dark state and demagnetization cooling.