Computation of Forces and Torques on Clusters of Micron-Sized Spheres in Optical Tweezers

Optical tweezers are a focused laser beam that exerts forces and torques on micrometer-sized particles. Calculations of optical forces on non-spherical particles whose size is comparable to the wavelength of the trapping beam are challenging. Here, we use a T-matrix code to calculate how clusters of spheres scatter light. The resulting T-matrix is exported to a software package that calculates optical forces and torques. We present calculations of optical forces and torques on clusters of two and three spheres. We discuss how the forces and torques depend on the orientation, size, and refractive index of the clusters.