Light-driven molecular motor

An all-optical control of light-angular-momentum transfer to nematic-liquid-crystal molecules is carried out by two copropagating noncoherent waves of orthogonal circular polarization. This allows the continuous variation of the total angular momentum of the light while conserving its circular symmetry. The molecular precession frequency is thus effectively and thoroughly controlled. The light-induced molecular reorientation threshold is shown to depend significantly on the azimuthal symmetry of the excitation light, while remaining the same for different values of its total angular momentum.