Field-free molecular orientation by an intense nonresonant two-color laser field with a slow turn on and rapid turn off

We propose a practical and versatile technique to achieve completely field-free molecular orientation with an intense, nonresonant, two-color laser field with a slow turn on and rapid turn off. The technique is based on the combined effects of both anisotropic polarizability interaction and anisotropic hyperpolarizability interaction. Using a FCN molecule as a sample, we show that the orientation achieved adiabatically by the peak of the laser pulse can be successfully revived at the rotational period of the molecule with the same degree of orientation. The crucial importance of the sufficiently slow turn on of the laser pulse is emphasized to achieve the highest possible degree of orientation.