Strong-field ionization of homonuclear diatomic molecules using orthogonally polarized two-color laser fields

Abstract

Using the improved molecular strong-field approximation we investigate high-order above-threshold ionization (HATI) of homonuclear diatomic molecules by an orthogonally polarized two-color (OTC) laser field. The OTC field components are linearly polarized, having the relative phase $\ensuremath{\varphi}$ and frequencies $r\ensuremath{\omega}$ and $s\ensuremath{\omega}$ ($r$ and $s$ are integers and $\ensuremath{\omega}$ is the fundamental frequency). The molecule is aligned in the laser-field polarization plane. We have found that for even values of $r+s$ the HATI spectra obey the ${C}_{2}$ rotational symmetry regardless of the relative phase, component intensities, and molecular orientation, while the spectra calculated for odd values of $r+s$ and for certain molecular orientations exhibit the reflection symmetry. We have also explored the symmetry transformations of the HATI spectra for a shift of the relative phase by ${180}^{\ensuremath{\circ}}$ and for various values of $r$ and $s$. These symmetries are illustrated by numerical examples of the HATI spectra of the ${\mathrm{N}}_{2}$ molecule. For particular values of the laser-field parameters, internuclear distance, and the electron emission angle we observed minima in the ionization yield as a function of the molecular orientation angle and the photoelectron energy. These minima are well fitted with the curve obtained using a condition for the destructive interference minima which we derived for an arbitrary laser field and applied to the OTC field. The relative phase between the OTC field components can be used to control the length and shape of the HATI plateau, as well as the appearance of these destructive interference minima.