Controlling ${\mathrm{H}}^{-}$ detachment with few-cycle pulses

We present a detailed analysis of short-pulse detachment processes using few-cycle pulses with the aim of demonstrating means for controlling such processes. We first generalize the standard Keldysh-type formalism for laser-target interactions (in which final-state interaction between the detached electron and the core is ignored) to include the possibility that the vector potential is nonzero at the end of the interaction between a short laser pulse and the target. With this formalism in hand, we examine the effects of half-cycle pulses (HCPs) on detachment of the prototypical negative ion ${\mathrm{H}}^{-},$ and show that detachment by pairs of oppositely-directed (i.e., “bidirectional”) HCPs allows one to understand the interference pattern seen in detachment by single-cycle pulses. We also examine in detail the transition from few-cycle pulses to many-cycle pulses as various experimental parameters are varied, i.e., the laser frequency, the laser-pulse duration, and the absolute phase of the carrier wave with respect to the pulse envelope. Finally, we examine the use of pairs of single-cycle pulses, differing in phase by $180°,$ together with a modest static electric field to control coherently the extent of ${\mathrm{H}}^{-}$ detachment as the delay between the pulses is varied. Our simulations show that this scheme allows one to modulate the ${\mathrm{H}}^{-}$ detachment probability by $\sim 30\%,$ which is far higher than has been achieved for similar schemes using many-cycle pulses. Although our results are presented specifically for ${\mathrm{H}}^{-},$ they apply to detachment of any negative ion having s-state valence electrons; in addition, the qualitative information on half-cycle, single-cycle, and few-cycle pulse interactions should be generally applicable to short-pulse detachment or ionization of other target atoms or ions.