Engineering Low-Power Cavity-Coupled Plasmonic Nanotweezers.

Plasmonic nanoapertures extend optical trapping into the subwavelength regime; but quantitative design rules remain limited because trapping is often inferred from spectral responses or field enhancement alone. This work establishes a full-field analysis framework for designing plasmonic nanoaperture tweezers under coherent illumination and experimental restrictions. We studied the plasmonic responses of three complementary plasmonic platforms-nanohole, nanohole-nanodisk, and cavity-coupled nanohole-nanodisk arrays-and their nanotrapping performance on dielectric and metallic nanoparticles using three-dimensional electromagnetic simulations and Maxwell stress tensor calculations. The results show that the force landscape in the particle volume depends strongly on the plasmonic resonance strength, the nanoparticle material, and the interaction with the target nanoparticle. In particular, we found that the cavity-coupled plasmonic array represents the most promising nanotrapping platform, capable of stable nanotrapping of metallic nanoparticles even under low power budgets and modest optical systems. Finally, we introduce a multi-criteria figure of merit (FoM) to compare trade-offs among trap stability, particle detuning effects, optical load, and nanoparticle material response. These results provide design guidance for compact, low-input-power plasmonic nanotweezer devices.