Optical trapping of nanowires

The ability to hold and manipulate nanowires using optical beams opens up a range of applications from force sensing to directed assembly. For this reason, optical trapping of nanowires has received much recent interest. In the following article we present a detailed computational investigation of the stability and general behaviour of these systems. It is found that relatively high index wires can be trapped. Furthermore, the properties of the trap vary with the parameters of the nanowire in characteristic ways. For example, the trap stiffness in the direction parallel to the axes of the beam and the wire falls off with increasing length, and can be made arbitrarily small. At the same time the other translational stiffness coefficients attain a limit in which the stiffness perpendicular to the polarization direction is approximately one half of that in the parallel direction. Rotational stiffness coefficients are seen, conversely, to increase steadily with length. These observations are explained in terms of a simple analytical model that supports the numerical calculations.