Doppler-free spectroscopy of metastable calcium in a discharge heat pipe

Abstract

We report on Doppler-free frequency modulation spectroscopy and polarization spectroscopy in a discharge heat pipe of yet unexplored transitions connecting the metastable ${}^{3}P_2\left(4s4p\right)$ state of calcium atoms with the multiply excited states ${}^{3}P_2\left(4p4p\right)$ and ${}^{3}D_3\left(4s3d\right)$. Calcium vapor is efficiently produced in a heat pipe operating in a small Pyrex cell filled with $2\text{torr}$ of neon. A dc discharge running at $500\mathrm{V}$ efficiently populates the metastable triplet states. Narrow resonances with bandwidths of a few tens of MHz with excellent signal-to-noise ratios are observed, well suited as references for laser frequency stabilization. Examination of the Zeeman shifts lets us determine the Landé $g$ factors of the excited states and compare them with the predictions based on the Russel-Saunders coupling scheme. We describe an economic, simple, and robust experimental setup that should work for other alkaline-earth-metal atoms like Mg and Sr, as well as for other solid elements with insufficient vapor pressures at room temperature.