Measurement of the non-linear Stark effect in hydrogen-like He+, n=4

Abstract
Anticrossing signals S-D and S-F in n=4 of He+ show a distinct shift with the static electric field applied to induce the signals. This allows investigation of the non-linear 'Stark effect of the fine structure' at electric fields of 50 to a few hundred V cm-1, a region inaccessible to experiment so far. Within the present accuracy the results agree with calculations based on a diagonalization of the energy matrix in crossed magnetic and electric fields.