Doppler-Free Two-Photon Spectroscopy of Hydrogen1S−2S

Abstract

We have observed the $1S\ensuremath{-}2S$ transition in atomic hydrogen and deuterium by Doppler-free two-photon spectroscopy, using a frequency-doubled pulsed dye laser at 2430 \AA{}. Simultaneous recording of the absorption spectrum of the Balmer-$\ensuremath{\beta}$ line at 4860 \AA{}, using the fundamental dye-laser output, allowed us to precisely compare the energy intervals $1S\ensuremath{-}2S$ and $2S$, $P\ensuremath{-}4S$, $P$, $D$ and to determine the Lamb shift of the $1S$ ground state to be 8.3 \ifmmode\pm\else\textpm\fi{} 0.3 GHz (D) and 8.6 \ifmmode\pm\else\textpm\fi{} 0.8 GHz (H).