Stark effect of atomic Helium singlet lines

We present experimental and theoretical investigations of the He spectral series 2(1)S - n(1)Q (n = 3 divided by 9, Q = S, P, D, ... , n - 1) and 2(1)P - n(1)Q (n = 3 divided by 9, Q = S, P, D, ... , n - 1) in electric fields up to 1635 kV/cm. Apart from the allowed transitions with vertical bar Delta L vertical bar = 1, the transitions with vertical bar Delta L vertical bar = 0, 2, 3, ... -without field strictly forbidden-were observed. Several He patterns become similar to hydrogen patterns, which means they are nearly symmetric and show in higher fields nearly linear Stark shifts. The applied fields are high enough that patterns belonging to neighboring principal quantum numbers (for n > 6) begin to overlap, which leads to interesting level-anticrossing effects. The experimental results are compared with numerical calculations, taking into account mixing between states of different principal quantum numbers and between singlet and triplet states. The agreement between experimental and theoretical results is quite good. (C) 2012 Optical Society of America