Investigation of the middle-energy region of the above-threshold ionization spectrum in a few-cycle laser field

Abstract

We use the improved strong-field approximation (ISFA) theory to investigate the evolution of the energy spectra with the carrier-envelope phase (CEP) of a few-cycle laser pulse. The theoretical calculations are consistent with the experimental measurements performed by Lindner et al (2005 Phys. Rev. Lett. 95 040401) which can be attributed to the scattering electrons whose ionization rates are modulated by the CEP of the laser pulse. We further investigate the dynamic behavior of the relevant scattering electrons by a Wigner distribution-like function based on the ISFA. Our analysis indicates that the zeroth-return forward-scattering electrons that move directly to the parent ion after tunneling and scatter forward with the parent core play a key role in the energy range of 2U p ∼ 4U p and the backward-scattering electrons are responsible for the high-energy region. Meanwhile, it is found that the contribution of the second-return backward-scattering electron to the middle energy spectrum is also important in the few-cycle laser field case.