Electromagnetic forces on a discrete spherical invisibility cloak under time-harmonic illumination.

We study electromagnetic forces and torques on a discrete spherical invisibility cloak under time-harmonic illumination. We consider the influence of material absorption and losses, and we show that while the impact of absorption on the optical force remains confined to frequencies near the absorption peak, its impact on the electromagnetic torque experienced by the cloak is spectrally broader and follows the spectrum of the absorption cross section of the cloak. We also investigate the mechanical shielding of a test particle within the cloak. We find that even an imperfect cloak can reduce the radiation pressure on the particle significantly; however, under certain conditions the force on the particle can be stronger than it would be in the absence of the cloak.