Precision measurement of the 1S Lamb shift and of the 1S-2S isotope shift of hydrogen and deuterium

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 Balmer-β 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 rclativistic nuclear recoil contribution to hydrogenic energy levels.