Figure 1: Enhanced ionization scenario and the angular streaking concept.
From: Probing the tunnelling site of electrons in strong field enhanced ionization of molecules
(a,b) Field-dressed potentials (orange surfaces) of a model diatomic molecule ion at (a) short and (b) large (critical) internuclear distances. In the latter case, the electron (green blob) nonadiabatically localized in the up-field potential well is more favourable to be freed through the narrow and low inner barrier when the molecule stretches to the critical internuclear distance. (c) Sketch of the angular streaking concept and our coordinate system. Owing to the streaking of the elliptically polarized laser pulse (red helix), an electron will receive a final momentum (green arrows) oriented perpendicular to the laser field (violet arrows) at its tunnelling. The instantaneous laser field vector at the moment of ionization hence can be retrieved from the streaked electron momentum pe (green arrows) or its recoil on the ion sum momentum psum (orange arrows). The olive helices in the dashed insets show sample momentum trajectories of the driven electron during the pulse. The ejection direction of the ionizing centre or molecular orientation (orange blobs) is derived from the relative momentum between the fragment ions prel (blue arrows).
