Optimising the optical forces from patterned actuators

Extremely large forces and torques have been reported when light is scattered by 2-dimensional metamaterial surfaces. Potential applications include force actuators in optically driven micro-machines, and diffractive solar sails. Here we consider refractive-index patterning of a dielectric substrate achieved photo-lithographically and demonstrate, using a computational electromagnetic approach, how a periodic structure may be optimised to maximise the optical forces and torques generated. We will show that enhancements of two orders of magnitude in the optical force are available in specific cases.