Geometrical optics calculation of forces and torques produced by a ringed beam on a prolate spheroid

The axial and transverse optical forces and torques exerted by circularly ringed beams on an arbitrarily oriented and homogeneous spheroid are calculated and studied within the framework of the geometrical optics regime. The results are applied to study the behavior of the forces in a counter-propagating optical trap. We calculate the trapping efficiencies and torques for several values of physical parameters, including the beam waist separation distance, the equivalent spheroid radius, the spheroid eccentricity, and the refractive index ratio between the particle and the surrounding medium. (C) 2010 Optical Society of America