Laser-spectroscopy measurement of the fine-structure splitting23P1–23P2ofHe4

Abstract

Laser spectroscopy has been performed on a beam of neutral $^{4}\mathrm{He}$ atoms. By using transverse laser cooling and focusing, we are able to prepare a bright beam of atoms in the metastable state $2\phantom{\rule{0.16em}{0ex}}{}^{3}{S}_{1}$ deflected from the original effusive atomic beam. The initial state preparation is completed with optical pumping on the $2\phantom{\rule{0.16em}{0ex}}{}^{3}{P}_{1}\ensuremath{\leftarrow}2\phantom{\rule{0.16em}{0ex}}{}^{3}{S}_{1}$ transition at the wavelength of 1083 nm, followed by laser spectroscopy on the $2\phantom{\rule{0.16em}{0ex}}{}^{3}{P}_{1,2}\ensuremath{\leftarrow}2\phantom{\rule{0.16em}{0ex}}{}^{3}{S}_{1}$ transitions. The $2\phantom{\rule{0.16em}{0ex}}{}^{3}{P}_{1}\ensuremath{-}2\phantom{\rule{0.16em}{0ex}}{}^{3}{P}_{2}$ fine-structure splitting is determined to be $2\phantom{\rule{0.16em}{0ex}}291\phantom{\rule{0.16em}{0ex}}177.69\ifmmode\pm\else\textpm\fi{}0.36\phantom{\rule{0.16em}{0ex}}\mathrm{kHz}$. The quantum interference effect is included in data extraction. This is the most precise laser spectroscopy measurement of the interval. Our result is in agreement with both the latest QED-based calculation and the most precise measurement conducted with microwave spectroscopy.