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 $^{3}P_{2}(4s4p)$ state of calcium atoms with the multiply excited states $^{3}P_{2}(4p4p)$ and $^{3}D_{3}(4s3d)$. Calcium vapor is efficiently produced in a heat pipe operating in a small Pyrex cell filled with $2\phantom{\rule{0.3em}{0ex}}\text{torr}$ of neon. A dc discharge running at $500\phantom{\rule{0.3em}{0ex}}\mathrm{V}$ 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 Land\'e $g$ 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.