Analytic solution to wave packet dynamics in a laser field: the case of linear chirp

NONADIABATIC TRANSITION AND CHEMICAL DYNAMICS: MULTI-DIMENSIONAL TUNNELING THEORY AND APPLICATIONS OF THE ZHU–NAKAMURA THEORY

Tunneling and nonadiabatic transition are the most important quantum mechanical effects in chemical dynamics. They are important not only for understanding the dynamics properly, but also for controlling molecular functions. The Zhu–Nakamura (ZN) theory can be combined with the quasi-classical trajectory method and with the IVR(Initial Value Representation)-type semiclassical theory to deal with large chemical systems. Laser control of molecular processes and control of molecular functions can also be realized by properly controlling nonadiabatic transitions. Furthermore, we have recently formulated an accurate theory for evaluating tunneling splitting and tunneling decay rate in multi-dimensional systems and also developed an efficient method to find caustics in multi-dimensional space. These methods combined with the ZN theory are expected to clarify various large scale chemical dynamics. This is a short review article on our recent activities mentioned above.

Nonlinear responses of degenerate two-level systems to intense few-cycle pulses

Population transfers in degenerate (or almost degenerate) two-level systems interacting with the few-cycle laser pulse are investigated. A simple and analytical formula of nonadiabatic transition probability is derived with completely degenerate condition, demonstrating the sensitive dependence of the transition probability on the phase of the few-cycle pulses. As one of the applications of this formula, a new way of controlling the nuclear wave packet dynamics at a potential curve crossing by 1 cycle laser pulse is proposed.

Control of nonadiabatic dissociation dynamics with the use of laser-induced wave packet interferences

Based on wave packet interferences induced by a stationary laser field, a simple way of controlling nonadiabatic dissociation dynamics is proposed. We treat a simple two-state model of diatomic molecules. In this model, there exist two dissociative potential energy curves which cross and are strongly coupled at an internuclear distance, and thus dissociations into one channel are predominant. We propose a control scheme to selectively dissociate a molecule into any favorite channel by choosing the laser frequency and intensity appropriately. The semiclassical estimation of desirable laser parameters can be performed easily by regarding the dissociation processes as nonadiabatic transitions between the Floquet states. The agreement between the semiclassical estimation and the quantum wave packet calculation is found to be satisfactory in the high frequency region (> or =1000 cm(-1)) where the Floquet state picture is valid. In the low frequency region (<1000 cm(-1)), on the other hand, there are discrepancies between them due to the invalidity of the Floquet picture and the dissociation probability is sensitive to the laser phase. This control scheme is applied to the predissociation dynamics of NaI, NaI-->Na+I.