Nonresonant above-threshold ionization by circularly polarized subpicosecond pulses

Abstract

Recent experiments show that above-threshold ionization (ATI) with intense linearly polarized light occurs via Stark-shifted bound-state resonances. Under identical conditions, we find that ATI with subpicosecond circularly polarized light is nonresonant. Unlike longer-pulse experiments, these spectra directly show the ionization rate versus intensity, and can therefore test ATI theories without deconvolving the inhomogeneous laser focus. Keldysh-Faisal-Reiss calculations do not agree with these new experimental results.