Double-resonance polarization spectroscopy using modulation sidebands

Abstract
A novel technique for ultrahigh-resolution laser spectroscopy is described. Coherence between atomic substates created by an amplitude-modulated light beam is monitored in transmission of a weak probe beam by polarization-selective optical heterodyne detection. As a demonstration, the technique is applied to Zeeman sublevels of the sodium ground state. The width (FWHM) of the observed resonances corresponds to 60 kHz.