Direct photodetachment of F−by mid-infrared few-cycle femtosecond laser pulses

Abstract

The recent adiabatic saddle-point approach of Shearer et al. [Phys. Rev. A 84, 033409 (2011)] is extended to multiphoton detachment of negative ions with outer $p$-state electrons. This theory is applied to investigate the strong-field photodetachment dynamics of F${}^{\ensuremath{-}}$ ions exposed to few-cycle femtosecond laser pulses, without taking into account the rescattering mechanism. Numerical calculations are considered for mid-infrared laser wavelengths of 1300 and 1800 nm at laser intensities of 7.7 $\ifmmode\times\else\texttimes\fi{}$ 10${}^{12}$, 1.1 $\ifmmode\times\else\texttimes\fi{}$ 10${}^{13}$, and 1.3 $\ifmmode\times\else\texttimes\fi{}$ 10${}^{13}$ W/cm${}^{2}$. Two-dimensional momenta saddle-point spectra exhibit a distinct distribution in the shape of a ``smile'' in the complex-time plane. Electron momentum distribution maps of direct electrons are investigated. These produce a distinct pattern of above-threshold detachment (ATD) concentric rings due to constructive and destructive quantum interference of electrons detached from their parent ions. Probability detachment distributions presented, capturing the influence of saturation effects that are found to become more significant with increasing laser intensity at a fixed wavelength. ATD photoangular distributions as functions of laser intensity and wavelength near channel closings are also investigated and found to be sensitive to initial-state symmetry. Nonmonotonic structures observed in the ejected photoelectron energy spectra are attributed to interference effects from coherent electronic wave packets. Additionally the profiles of all the photoelectron emission spectra show strong dependence on the carrier-envelope phase, indicating that it is a reliable parameter for characterizing the wave form of the pulse.