Laser-sub-cycle two-dimensional electron-momentum mapping using orthogonal two-color fields

We study laser-sub-cycle control over electron trajectories concomitantly in space and time using orthogonally polarized two-color laser fields. We compare experimental photoelectron spectra of neon recorded by coincidence momentum imaging with photoelectron spectra obtained by semiclassical and numerical solutions of the time-dependent Schrödinger equation. We find that a resolution of a quarter optical cycle in the photoelectron trajectories can be achieved. It is shown that depending on their sub-cycle birth time the trajectories of photoelectrons are affected differently by the ion's Coulomb field.

Figure 1

(a) Electric fields of the 400-nm (blue) and 800-nm pulse. The colors encode quarter cycles of the 800-nm field. (b) Field-driven electron momentum $\vec{p}=-\vec{A}\left(t_0\right)$ for a single cycle of the OTC field in the plane of polarization for various phases $\Delta \phi$ between fundamental and second harmonic. (c) Measured electron-momentum distributions correlated to ${\mathrm{Ne}}^{+}$ in the $xz$-polarization plane of the OTC pulse with $|p_y|<0.1$ a.u. (d) Electron momentum spectra calculated the same way as those in (b) but with $\vec{p}\left(t_0\right)$ extracted from Fig. 2, thereby accounting for the parent ion's influence. The momentum $\vec{p}=-\vec{A}\left(t_0\right)$ is underlaid in gray.

Figure 2

Comparison of experimental (a) and calculated (b)–(d) electron-momentum distributions. (b) Solutions of the TDSE. (c),(d) CTMC simulations without (c) and with inclusion (d) of the ionic potential. See text for details.

Figure 3

(a)–(d) Electron momentum spectrum for $\Delta \phi =\pi$ simulated by CTMC with the ionic potential included, separated into the contributions from trajectories born during different quarter cycles of the OTC field, as indicated in the panels. (e)–(h) Average electron momentum $p_x\left(t_0\right)$ (red) and $p_z\left(t_0\right)$ (blue) over birth time $t_0$ calculated by CTMC, in comparison with $p_{x,z}=-A_{x,z}\left(t_0\right)$ (gray dashed and dotted-dashed lines, respectively) for various $\Delta \phi$ as indicated in the panels. The green full lines denote ionization rates [21] normalized to their respective maxima. Color coding of quarter cycles as in Fig. 1.