Study of non-hydrogenic near degeneracies between m sublevels in the linear Stark effect of sodium Rydberg states

Abstract
The authors have studied the linear Stark effect of sodium Rydberg states by subDoppler high resolution spectroscopy using a continuous stepwise excitation of sodium atoms (3S to 3P to 3D to nF) with the help of a CW dye laser and of two single-mode diode lasers. They have shown a quasidegeneracy of m=0, mod m mod =1 and mod m mod =2 states, revealing an unexpected non-hydrogenic behaviour of Stark states in this linear regime. A simple model, based on a 'truncated Stark basis' approach accounts for this feature, which is common to all alkali atom Rydberg states.
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