Observation and calculation of the Stark effect of Rydberg states of aluminum

Using double-resonance laser excitation, we obtained the spectrum of the nf Rydberg series of Al. The highest principal quantum number reached was 67; we believe this is the first work to reach this value. In a moderately strong external electric field, we observed Stark effect induced forbidden transition lines. The electric field strength was estimated with the concept of the classical ionization field; a hydrogen-like non-perturbative method was used to analyzed the Al Stark effect. The theoretical spectrum showed exact agreement with experiment.