Theory of Nanometric Optical Tweezers

We propose a scheme for optical trapping and alignment of dielectric particles in aqueous environments at the nanometer scale. The scheme is based on the highly enhanced electric field close to a laser-illuminated metal tip and the strong mechanical forces and torque associated with these fields. We obtain a rigorous solution of Maxwell's equations for the electromagnetic fields near the tip and calculate the trapping potentials for a dielectric particle beyond the Rayleigh approximation. The results indicate the feasibility of the scheme.