Photodetachment dynamics of F${}_2{}^{-}$ in a strong laser field

The angle-resolved photoelectron spectrum of F${}_2{}^{-}$, exposed to a strong infrared laser pulse, is significantly different from the spectrum of F${}^{-}$ obtained under the same experimental conditions. The experimental results are used to test the theory based on the molecular strong-field approximation. Both the dressed and the undressed versions of this theory fail to reproduce the F${}_2{}^{-}$ spectrum. One origin for this discrepancy is that photodetachment of F${}^{-}$ produced by strong-field dissociation of F${}_2{}^{-}$ needs to be considered.

Figure 1

Momentum distribution of photoelectrons detached from F${}_2{}^{-}$ (left) and F${}^{-}$ (right) in a laser field of 1300 nm wavelength and $3.4\times {10}^{13}$ W/cm${}^2$ peak intensity. $p_{\perp }$ and $p_{\parallel }$ represent the momentum components perpendicular and parallel to the laser polarization axis, respectively.

Figure 2

Potential energy curves of electronic states of F${}_2{}^{-}$ and the ground electronic state of F${}_2$. ${\nu }_i$ and ${\nu }_f$ are the vibrational quantum numbers of F${}_2{}^{-}$ and F${}_2$ vibrational states, respectively, $E_0$ denotes the threshold energy for a given ${\nu }_i\to {\nu }_f$ transition. The inset shows the squared overlap of nuclear wave functions, $S_{{\nu }_f{\nu }_i}^2$, for ${\nu }_i=0$ and different ${\nu }_f$ values.

Figure 3

Photoelectron distributions of F${}_2{}^{-}$ predicted by the dressed (left) and undressed (right) versions of the molecular SFA.

Figure 4

Energy distribution of photoelectrons emitted from F${}_2{}^{-}$ along the laser polarization axis. Circles represent experiment, solid and dashed lines show predictions by the undressed and dressed versions of the molecular SFA, respectively. The curves are normalized according to the integrated yield.

Figure 5

Comparison of the experimental energy distribution shown in Fig. 4 (circles) with predictions by the model that assumes strong-field dissociation of F${}_2{}^{-}$ followed by photodetachment of F${}^{-}$. Calculations are performed for different initial times (see text): $-{\sigma }_t$ (dotted line), $-{\sigma }_t/2$ (dashed line), and 0 (solid line). The curves are normalized according to the integrated yield.