Optical frequency measurements of6sS1∕22−6pP1∕22(D1)transitions inCs133and their impact on the fine-structure constant

Abstract

High resolution laser spectroscopy of the $6s\phantom{\rule{0.2em}{0ex}}^{2}S_{1∕2}\ensuremath{\rightarrow}6p\phantom{\rule{0.2em}{0ex}}^{2}P_{1∕2}$ transition (${D}_{1}$ line) in neutral $^{133}\mathrm{Cs}$ is performed in a highly collimated thermal atomic beam by use of a femtosecond laser frequency comb and narrow-linewidth diode laser. The diode laser is offset locked to a single frequency component of the femtosecond laser frequency comb and probes the optical transitions between selected pairs of ground-state and excited-state hyperfine components. A photodiode detects the excited-state decay fluorescence, and a computerized data acquisition system records the signal. The Doppler shift is eliminated by orienting the laser beam in a direction perpendicular to the atomic beam to within a precision of $5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}\phantom{\rule{0.3em}{0ex}}\mathrm{rad}$. Optical frequencies for all four pairs of hyperfine components are measured independently, from which the ${D}_{1}$ line centroid and excited-state hyperfine splitting are obtained by least-squares minimization with the ground-state splitting as a fixed constraint. We find the ${D}_{1}$ line centroid to be ${f}_{{D}_{1}}=335\phantom{\rule{0.2em}{0ex}}116\phantom{\rule{0.2em}{0ex}}048\phantom{\rule{0.2em}{0ex}}748.1(2.4)\phantom{\rule{0.3em}{0ex}}\mathrm{kHz}$, and the $6p\phantom{\rule{0.2em}{0ex}}^{2}P_{1∕2}$ state hyperfine splitting to be 1 167 723.6(4.8) kHz. These results, in combination with the results of an atom interferometry experiment by Wicht et al. [Phys. Scripta T 102, 82 (2002)], are used to calculate a new value for the fine-structure constant.