Lagrangian descriptor and escape time as tools to investigate the dynamics of laser-driven polar molecules

We consider the nonlinear dynamics of a diatomic polar molecule under a linearly polarized laser field. We assume a model in which the molecule dipole is coupled with a time-dependent electric field. This system presents a bound energy region where the atoms are bound, and a free-energy region where the atoms are dissociated. Due to the nonalignment between the dipole axis and the laser direction, and the time dependence of the external field, this system presents two and a half degrees of freedom, namely the vibrational degree, the rotation degree, and the time. To investigate the system dynamics, instead of using the Poincare surfaceof-section technique, we propose the use of the Lagrangian descriptor associated with the escape times. The Lagrangian descriptor is a quantity that reveals complex structures in the phase space, whereas the escape times are the time span in which a trajectory is initially in the bound region before escaping to the unbound region. The combination of these two quantities allows us to distinguish between real stability regions from other complex structures, including stickiness regions, and a different formation, which we call escape islands. With the help of these tools, we find that for high-field amplitudes the inclusion of rotation leads to an increase of the stability regions, which implies a decrease of the dissociation in comparison with the one-dimensional case.

Automated summary

This article investigates the nonlinear dynamics of a diatomic polar molecule under a linearly polarized laser field. The molecule's dipole is coupled with a time-dependent electric field, resulting in a bound energy region and a free-energy region. The system has two and a half degrees of freedom due to the nonalignment between the dipole axis and the laser direction, as well as the time dependence of the external field. Instead of using the Poincare surface-of-section technique, the Lagrangian descriptor associated with escape times is proposed to analyze the system dynamics.