Mechanisms of optical angular momentum transfer to nematic liquid crystalline droplets.

A detailed study is presented that evaluates the relative importance of wave plate behavior, scattering processes and absorption phenomena in transferring optical torque from circularly polarized light to optically trapped nematic droplets. A wide range of parameters is considered: droplet diameters between 1 and 15 μm, birefringence values from 0.15 to 0.26 and trapping beam powers from 50 mW to 400 mW. Wave plate behavior is verified through the dependence of torque on droplet diameter and material birefringence. The dependence of the magnitude of the torque on material birefringence confirms the additional importance of the scattering mechanism. Absorption processes are found to be negligible.