Polarization-dependent non-uniform rotation rates of rhombohedral calcite

Catherine M. Herne, Johanna R. Levey, and Tom R. McCausland

We demonstrate the polarization-dependent torque on rhombohedral calcite in an optical trap. Our precipitate technique produces regular crystals approximately 10μm on all edges. The regularity of the crystal shape makes it possible to visually identify the optical axis as well as the orientation of the polarization axes. When a rhombohedral crystal is trapped in an elliptically polarized beam, it orients itself with its optic axis approximately parallel to the beam axis. While in this orientation, the total torque increases and decreases relative to three extraordinary and ordinary axes of the crystal. We measure this axis-dependent calcite rotation through video analysis and model the dependence of the torque on the crystal orientation. The ability to predict the motion of calcite gives an analytical tool for applications such as fluid stirring or “lab on a chip” systems.

DOI