Nondipole effects in tunneling ionization by intense laser pulses

Abstract

The limit of decreasing laser frequency cannot be considered independently from nondipole effects due to the increase in the laser-induced continuum electron speed in this limit. Therefore, in this work, tunneling ionization in the adiabatic limit is considered for an effective field that includes effects beyond the electric-dipole term to first order in $1/c$, with $c$ being the speed of light. The nondipole term describes the interaction resulting from the electric dipole-induced velocity of the electron and the magnetic-field component of the laser. The impact of this term on the ionization rate, tunnel exit point, momentum at the tunnel exit, and electron dynamics is discussed. In the appropriate limit, the results of a nondipole strong-field approximation approach and those of the strict adiabatic limit, where time and field strength are parameters, are discussed. The nondipole strong-field approximation approach is used to identify nonadiabatic modifications of the initial conditions. The results open up an avenue to include nondipole effects in the initial tunneling ionization step in semiclassical models of strong-field and attosecond physics.