Ultrashort-laser-pulse-mediated asymmetry in the branching of dissociated fragments of HD+: Effects of a weak third pulse and carrier envelope phase of the dissociating pulse

Abstract

We have numerically explored the possibility of controlling the branching ratio of the two distinguishable photodissociation products of HD${}^{+}$ (neutral D and neutral H) in an ultrashort laser field. In our multipulse scheme, a bound vibrational wave packet is generated in the ground electronic state of HD${}^{+}$ by vertical ionization from the ground state of HD. The control pulse acts on this wave packet at different time delays after the wave-packet generation is completed. It was found that, for a broad range of delay times between the pump pulse and the control pulse, any possible asymmetry in the branching ratio disappears due to the nonadiabatic coupling effects present in HD${}^{+}$. A third pulse, termed the driving pulse, with a relatively longer duration and a much weaker field strength, is introduced to counterbalance the nonadiabatic effects relevant for this heteronuclear system and to guide the dissociative reaction to a specific product channel. In fact, we have shown that the application of the driving pulse reproduces the branching-ratio pattern obtained on variation in the interpulse delay time between the pump pulse and the control pulse in the absence of the nonadiabatic coupling effects. The role of both the delay time between the pump pulse and the control pulse as well as the carrier envelope phase effects of the optical field of the control laser on the branching ratios in the two reaction channels were studied. The robustness of the driving pulse mediated asymmetry control, and any possible introduction of asymmetry by the driving pulse itself were also investigated.