Field-free molecular orientation by femtosecond dual-color and single-cycle THz fields

We theoretically demonstrate the dynamics of field-free molecular orientation under the radiation of a femtosecond dual-color field and a delayed single-cycle terahertz (THz) field, with CO and LiH as the prototype molecules. The results show that the impulsive Raman processes of dual-color field and the resonant effect of the THz field exhibit higher excitation efficiency in a combined way and give rise to a significant enhancement of orientation degree when the THz field is introduced around the full revival time of molecules. It also shows that the dual-color field has an advantage over the single-color field when they combine with the THz field in creating field-free orientation.