Optical forces on a Mie spheroidal particle arbitrarily oriented in a counterpropagating trap

The axial and transverse optical forces exerted by Gaussian beams on an arbitrarily oriented and homogeneous spheroid are calculated and studied within the framework of the Mie theory. The results are applied to study the behavior of the forces in a counterpropagating optical trap. We calculate the trapping efficiencies for a wide range 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) 2009 Optical Society of America