Precision measurement of the1SLamb shift and of the1S−2Sisotope shift of hydrogen and deuterium

Abstract

A precision measurement of the $1S$ Lamb shift of atomic hydrogen and deuterium, using high-resolution laser spectroscopy is reported. The $1S-2S$ transition was observed by Doppler-free two-photon spectroscopy, using a single-frequency cw dye laser near 4860 Å with a nitrogen-pumped pulsed dye amplifier and a lithium formate frequency doubler. The $n=2-4\mathrm{}$ Balmer-$\beta$ line was simultaneously recorded with the fundamental cw dye-laser output in a low-pressure glow discharge, using sensitive laser polarization spectroscopy. From a comparison of the two energy intervals a ground-state Lamb shift of 8151±30 MHz has been determined for hydrogen and 8177±30 MHz for deuterium, in agreement with theory. The same experiments yield a tenfold improved value of the $1S-2S$ isotope shift 670992.3±6.3 MHz and provide the first experimental confirmation of the relativistic nuclear recoil contribution to hydrogenic energy levels.