We investigate analytically and numerically the lateral optical binding force in non-Hermitian nanoparticle dimers with gain-assisted active response. In comparison with conventional plasmonic or dielectric nanostructures with passive behavior, the lateral binding force in an active dimer can be dynamically controlled by the external pumping level. Within a linear-response gain model, we show that in close proximity to a critical point the gain-assisted system can exhibit strong enhancement of the lateral binding force, switching between attractive and repulsive regimes, and the emergence of a pronounced transverse driving force. A variety of configurations are analyzed and discussed, including homo-/heterodimers made from multiple material components, different size parameters in geometry, and varying plane-wave illumination. The forces between the dimer structure are calculated using the Lorentz-force approach in the coupled dipole approximation, as well as rigorous numerical simulation using Maxwell stress tensor formalism, combined with the multiple-multipole scattering theory or a finite-element solver. The results provide a theoretical framework for gain-assisted control of optical forces at the nanoscale and clarify the physical scope of the predicted enhancement for future studies of optically bound matter.

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• Dipolar interaction
• Optical forces
• Optical pumping
• Photonics
• Scattering theory
• Nanoparticles