Continuous rotational motion in birefringent particles using two near-orthogonally polarized optical tweezers beams at different wavelengths with low ellipticity

Continuous yaw ( in-plane) rotation of an optically trapped birefringent particle is conventionally achieved by illuminating with light of high ellipticity. This ellipticity has to be high enough to make the tilt of the washboard potential bypass the confining effect of the corrugation. Here by using a novel technique, we generate continuous rotations of a 3 µm sized spherical birefringent particle with ellipticity lower than that permissible with a single optical tweezers beam. We use two lasers, near-orthogonally polarized, with similar intensities at wavelengths of 1064 nm and 975 nm to obtain continuous rotations, just by making one of the beams elliptically polarized, but well lower than that permissible by the washboard potential. The maximum rotation frequency we achieve with the present configuration is 4.5 Hz which can be increased by simultaneously increasing the two laser intensities .