Molecular potential anisotropy probed by electron rescattering in strong-field ionization of molecules

Abstract

One of the main differences between rescattering following laser-induced ionization of atoms and molecules and electron-ion collisions performed with electron beams is the quivering dynamics of the electron around the ionic site in laser experiments. This report is aimed at probing the effect of the anisotropic potential of linear and symmetric molecular ions on the departing electron following tunnel ionization and rescattering by an intense femtosecond laser field at $0.8\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{m}$ and ${10}^{14}{\phantom{\rule{3.33333pt}{0ex}}\mathrm{Wcm}}^{\ensuremath{-}2}$. The laser excitation conditions are chosen so that the maximum collision energy remains of the order of 20 eV. In the energy range where rescattering is significant, the angular widths of the photoelectron angle-resolved energy spectra are found to be significantly larger for ${\mathrm{N}}_{2}$ and ${\phantom{\rule{3.33333pt}{0ex}}\mathrm{C}}_{2}{\mathrm{H}}_{2}$ molecules aligned perpendicularly to the laser polarization than the angular widths of angle-resolved energy spectra recorded in parallel alignment, although ${\mathrm{N}}_{2}$ and ${\phantom{\rule{3.33333pt}{0ex}}\mathrm{C}}_{2}{\mathrm{H}}_{2}$ obey opposite tunnel ionization dynamics with respect to alignment. In the associated collision energy and angle ranges where this effect is observed, the lowest values of the impact parameter are less than one atomic unit. It is conjectured that the approach of the quivering departing electron may be sufficient for its trajectories to be dependent on the molecular ion core alignment, i.e., the anisotropic molecular potential.