Control of photodissociation with dynamic Stark effect induced by Thz pulses

Abstract

We demonstrate how dynamic Stark control (DSC) can be achieved on molecular photodissociation in the dipole limit, using single-cycle (FWHM) laser pulses in the terahertz (THz) regime. As the laser-molecule interaction follows the instantaneous electric field through the permanent dipoles, the molecular potentials dynamically oscillate and so does the crossings between them. In this paper, we consider rotating-vibrating diatomic molecules (2D description) and reveal the interplay between the dissociating wave packet and the dynamically fluctuating crossing seam located in the configuration space of the molecules spanned by the R vibrational and $θ$ rotational coordinates. Our showcase example is the widely studied lithium-fluoride (LiF) molecule for which the two lowest $Σ$ states are nonadiabatically coupled at an avoided crossing (AC), furthermore a low-lying pure repulsive $Π$ state is energetically close. Optical pumping of the system in the ground state thus results in two dissociation channels: one indirect route via the AC in the ground $Σ$ state and one direct path in the $Π$ state. We show that applying THz control pulses with specific time delays relative to the pumping, can significantly alter the population dynamics, as well as, the kinetic energy and angular distribution of the photofragments.