Significant optical force enhancements of nanostructure with balanced gain and loss

In this paper, we theoretically analyze the optical force between a pair of active and passive plasmonic core-shell nanoparticles (NPs). The optical force between the NPs can be either attractive or repulsive near the critical point while the passive dimer provides only attractive force. We reveal that the reversal of attractive or repulsive force is determined by the relative phase of electric dipole (ED) modes, which can be strongly affected by the gain and loss coefficient.. Compared with the passive dimer with the same size, the active-passive dimer can exhibit a very high repulsive force (about two orders of magnitude) while remaining the same order magnitude attractive force when the value of coefficient is 0.345. Interestingly, we find that the position of the maximum repulsive force occurs near the critical point. We also investigate the influence of variations in geometrical parameters of the dimer and polarization angle on the force. Finally, the numerical results demonstrate that when the dimer is illuminated by a laser beam, the attractive and repulsive forces can also be achieved. The manipulation of optical force can find potential in optical sorting and transport of NPs. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Automated summary

The optical force between a pair of active and passive plasmonic core-shell nanoparticles (NPs) is theoretically analyzed in this paper. The reversal of attractive or repulsive force is determined by the relative phase of electric dipole modes, which can be strongly affected by the gain and loss coefficient. The active-passive dimer can exhibit a very high repulsive force compared to the passive dimer with the same size under certain coefficient values, while the passive dimer provides only attractive force. This manipulation of optical force has potential applications in optical sorting and transport of NPs.