Moiré patterns in doubly differential electron-momentum distributions in atomic ionization by mid-infrared lasers

Abstract

We analyze the doubly differential electron momentum distribution in above-threshold ionization of atomic hydrogen by a linearly-polarized mid-infrared laser pulse. We reproduce side rings in the momentum distribution with forward-backward symmetry previously observed by Lemell \textit{et al.} in Phys. Rev. A \textbf{87}, 013421(2013), whose origin, as far as we know, has not been explained so far. By developing a Fourier theory of moir\'{e} patterns, we demonstrate that such structures stems from the interplay between intra- and intercycle interference patterns which work as two separate grids in the two-dimensional momentum domain. We use a three dimensional (3D) description based on the saddle-point approximation (SPA) to unravel the nature of these structures. When the periods of the two grids (intra- and intercycle) are similar, principal moir\'{e} patterns arise as concentric rings symmetrically in the forward and backward directions at high electron kinetic energy. Higher order moir\'{e} patterns are observed and characterized when the period of one grid is multiple of the other. We find a scale law for the position (in momentum space) of the center of the moir\'{e} rings in the tunneling regime. We verify the SPA predictions by comparison with time-dependent distorted wave strong-field approximation (SFA) calculations and the solutions of the full 3D time-dependent Schr\"{o}dinger equation (TDSE).