Scaled-energy spectroscopy of argon atoms in an electric field

We have measured the scaled-energy absorption spectra of argon Rydberg states in a uniform electric field. The experiment utilized laser spectroscopy from the metastable 4s[3/2]2 state in a fast atom beam. The scaled absorption spectra are Fourier transformed to obtain recurrence spectra that allow semiclassical analysis. Argon recurrence spectra reveal bias towards populating downhill-oriented classical trajectories and show large-scale modulations. A quantum calculation indicates that the asymmetric trajectory distribution is caused by the large p-quantum defect and that d-f excitation from the initial metastable state is influential in shaping the observed oscillations in the recurrence maps. The analysis serves to highlight the correspondence between quantum oscillator strengths and classical orbits