Suppression of multiphoton intrashell resonances in Li Rydberg atoms

Abstract

Multiphoton intrashell transitions in strongly driven Li ($n=25$) Rydberg atoms are studied experimentally. Orthogonal dc electric and magnetic fields lift the degeneracy of the $n$ shell and define the eccentricity $e$ of the initial coherent elliptic states, which are formed by laser excitation and subsequent adiabatic transformation. The intrashell transitions are driven by a time-harmonic electric field linearly polarized parallel to the major axis of the ellipse. $N$-photon resonances with $N=1\ensuremath{-}9$ are studied as a function of $e$. All resonances with $N\ensuremath{\geqslant}3$ are suppressed at certain $e$ values in between $0$ and $1$. A similar system was analyzed by Yabuzaki et al. [Phys. Rev. A 10, 1955 (1974)] who found a simple pattern of suppressions that applies also for the present experiments. The results of these experimentally confirm that each time $N$ is increased by two, an additional suppression is observed.