Signatures of tunneling and multiphoton ionization in the electron-momentum distributions of atoms by intense few-cycle laser pulses

Abstract

Electron-momentum distributions for above-threshold ionization of argon in a few-cycle, linearly polarized laser pulse are investigated. Spectral features haracteristic of multiphoton as well as tunneling ionization coexist over a range of the Keldysh parameter in the transition regime 1. Surprisingly, the simple strong-field approximation SFA is capable of reproducing the key features of the two-imensional momentum distributions found in the full solution of the time-dependent Schrödinger equation, despite the fact that SFA is known to severely underestimate the total ionization probability.