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High-resolution spectroscopy of the 1S-2S transition of atomic hydrogen and deuterium.

Two-photon spectroscopy of the hydrogen 1[ital S]-2[ital S] transition in a cold atomic beam has reached a resolution [Delta][nu]/[nu] of 1 part in 10[sup 11] in hydrogen and 7 parts in 10[sup 12] in deuterium. The hydrogen and deuterium 1[ital S]-2[ital S] transition frequencies have been determined with a precision of 1 part in 10[sup 11]. This leads to an accurate value for the Rydberg constant, while the 1[ital S] Lamb shift and the isotope shift are determined with order of magnitude improvements over previous measurements. We describe in detail the 1[ital S]-2[ital S] spectrometer, calculate the line shape of the resonance, and compare it to the experimental data.