Wavepacket-interference view of optical excitation

Abstract

Abstract Excitation mechanisms using intense lasers are described as being either a multiphoton or tunneling process, based on whether the Keldysh parameter γ is greater than or less than unity. However, the lack of intrinsic connection between these two excitation mechanisms fetters the cognizance of dynamics in strong field ionization under typical experimental conditions. In this paper, quantum tunneling and the multiphoton process are connected by an intuitive picture of wavepacket interference. In this view, the transition from multiphoton resonance to tunneling is recognized as a decoherence process of tunneling electrons. We reveal this decoherence in crystals and gases when the Keldysh parameter decreases. In this process, the characteristics of driving fields, frequent scattering in crystals and localization play an important role. Moreover, once this understanding of multiphoton resonance is obtained, additional means are provided for coherent control in electron excitations. We find that the interference of tunneling electrons leads to novel performances of the transition rate in subcycles, and provides a theoretical method of attosecond-resolved quantum interference control. Our work opens up a new prospect of electron ultrafast control.