Observation of a transition in the dynamics of strong-field atomic excitation

Abstract

The consensus on the mechanism of atomic excitation in an intense laser field has not been reached so far because the proposed mechanisms may dominate in different regimes. In this paper, we show a clear transition of the underlying physical mechanism of strong-field atomic excitation from multiphoton resonance to coherent recapture by investigating the intensity dependence of the yields of neutral excited atoms (Ar∗) and singly charged ions (Ar+) of argon experimentally and theoretically. Our results indicate that, for 400 nm, the multiphoton resonance mechanism plays a significant role at low intensity and coherent recapture mechanism becomes important at high intensity. While for 800 nm, distinctive out-of-phase oscillations of Ar∗ and Ar+ yields are identified, implying that coherent recapture mechanism dominates. Our work provides a more comprehensive understanding of the atomic excitation mechanism in an intense laser field.