Avoided level crossings in bound Rydberg states of barium in an electric field

In a CW laser experiment on bound Rydberg states of barium electric-field-induced level crossings were studied. A regular type of avoided crossing of 6snf ³ F ₂ and 6s (n+4)s ³ S ₁ levels (n≈60,M=0) was observed under circumstances where the minimum separation was larger than the linewidth involved. This type of crossing could be reproduced using a diagonalisation procedure of the total energy matrix in the presence of the field. However, in the case of avoided crossings of the 6snf ³ F ₂ and 6s(n+4)p ¹ P ₁ sublevels, where the minimum separation was smaller than the linewidth of the³ F ₂ level, an interference-like profile was recorded. An important feature in the explanation of this interference-like profile turned out to be the broadening of the³ F ₂ level by small field inhomogeneities.