Laser Induced Field Free Molecular Rotation

 In practically all previous works in this field, the rotational motion is enhanced, but the net total angular momentum delivered to the molecules remained zero, and for a good reason. For a single pulse schemes, as well as for techniques using multiple pulses polarized in the same direction, no preferred sense of rotation exists due to the axial symmetry of excitation.  In our scheme we apply the first pulse, linearly polarized (red arrow) along the z axis and let the molecules rotate until they reach an aligned state. At the time of maximal alignment, the molecules are confined in a narrow cone around the polarization direction of the first pulse. At this moment, a second pulse, linearly polarized at 45 degrees to the first pulse, is applied, and thereby induces unidirectional (clockwise) molecular rotation. An interesting feature of this unidirectional rotational excitation is the confinement of the molecules to rotate mostly in the plane defined by the two polarizations.

Figure: schematic representation of the two pulse scheme for the induction of field-free unidirectional molecular rotation