Fast atomic beam separated oscillatory field radiofrequency spectroscopy is used to measure the fine structure of H, D, and He; molecular-beam laser spectroscopy is used to study the structure and decay mechanism for triplet Rydberg states of H2, HD, and D2; and various laser spectroscopy techniques are used to study the 2S1 - 2P0,1,2 interval in He3 and He4. The spectroscopy involves invention and development of very advanced high resolution techniques, and leads to definitive tests of quantum electrodynamics.
