We have extended the theory of the high-frequency Stark effect in atomic spectra to treat cases of multiple interacting upper levels and of strong electric fields and resonances, where perturbation theory is inadequate. We have also included the effects of a static external magnetic field both in the perturbation theory and the more general treatment. Numerical calculations are presented for the 4922- and 4388-Å lines of He i for several field strengths and frequencies. The new theory is used to infer the frequency and strength of a microwave electric field applied to a steady-state helium discharge with no magnetic field; excellent agreement is obtained between the calculated and the observed spectra.

• Received 6 July 1971

DOI:https://doi.org/10.1103/PhysRevA.5.490