High-order above-threshold ionization beyond the electric dipole approximation

Abstract

Photoelectron momentum distributions from strong-field ionization are calculated by numerical solution of the one-electron time-dependent Schrödinger equation for a model atom including effects beyond the electric dipole approximation. We focus on the high-energy electrons from rescattering and analyze their momentum component along the field propagation direction. We show that the boundary of the calculated momentum distribution is deformed in accordance with the classical three-step model including the beyond-dipole Lorentz force. In addition, the momentum distribution exhibits an asymmetry in the signal strengths of electrons emitted in the forward/ backward directions. Taken together, the two non-dipole effects give rise to a considerable average forward momentum component of the order of 0.1 a.u. for realistic laser parameters.

Holographic interferences in strong-field ionization beyond the dipole approximation: The influence of the peak and focal-volume-averaged laser intensities

“…Although the relativistic recollision parameter is rather small in our experiment, Γ R ≈ 7.4 × 10 −3 , the photoelectron momentum resolution in our experiment is sufficiently high to resolve the nondipole effect on the holography pattern of the order of δp z ∼ √ Γ R ∆ ⊥ = U p /c ∼ 2 × 10 −2 a.u.. The nondipole signature in the holographic interference pattern is the asymmetry with respect to the laser propagation direction: a nonuniform shift of the momentum distribution along the laser propagation direction, already noted in [15][16][17]. The shift fades out for vanishing longitudinal momenta.…”

Magnetic fields alter strong-field ionization

“…We follow the scheme presented in Ref. 21 such that the theory covers the dynamics within the electric quadrupole and magnetic dipole approximation. After applying a unitary transformation to the initial system in effective potential V for the argon atom is chosen as by Tong et al 34 , but with the singularity removed using a pseudopotential 35 for angular momentum l=1.…”

“…2 we follow the description from Ref. 21 highest intensity 1.1×10 14 W/cm², except that oscillations resulting from intra-cycle interferences are smoothed out and that the depth of the minima in the observables of Fig. 3 is slightly different.…”

Schrödinger formulation of the nondipole light-matter interaction consistent with relativity

“…The Hamiltonian (24), which contains all beyond dipole interaction terms up to and including order 1/c corrections, constitutes the main result of the present work. The alternative formulation ( 23) is reminiscent of the light-matter interaction derived recently by Brennecke and Lein [32] and used in explaining experimental data on magnetic field effects in the strong-field ionization of atoms [6]. In the nonrelativistic limit, and provided relativistic corrections of order (1/c) 2 and higher are unimportant to the dynamics, the two formu-lations ( 23) and ( 24) would yield similar but not identical results.…”