Abstract

We are measuring the Lamb shift of the IS hydrogen ground state as a test of quantum electrodynamics. In one half of the experiment, we observe the 1S-2S transition with high resolution using Doppler-free two-photon absorption. The required 243-nm light, generated by intra- cavity frequency doubling of a 486 nm ring dye laser, is coupled into a uv power-enhancement cavity. Atomic hydrogen flows through the waist of the laser field and the two-photon excitation of the atoms is monitored by detecting the collisionally-induced Lyman-α fluorescence. In a separate part of the experiment we excite the single-photon transition 2S–4P_1/2 or 2S–4P_3/2 at 486 nm in a collimated beam of metastable hydrogen, H(2S). The laser beam propagates at right angles to the atomic beam in order to reduce the Doppler shift and the resonance is observed as a depletion of the H(2S) population. The Doppler shift is further reduced by retro-reflecting the laser beam, and any remaining shift is measured by changing the beam crossing angle.

© 1994 IEEE