Optical trapping of nanoparticles with tunable inter-distance using a multimode slot cavity.

Optical trapping of nano-objects (i.e., the nano-tweezers) has been investigated intensively. Most of those nano-tweezers, however, were focused on the trapping of a single nanoparticle, while the interactions between them were seldom considered. In this work, we propose a nano-tweezers in a slot photonic crystal cavity supporting multiple modes, where the relative positions of two trapped nanoparticles can be tuned by selective excitation of different resonant mode. Results show that both the nanoparticles are trapped at the center of the cavity when the first order mode is excited. When the incident source is tuned to the second order mode, however, these two nanoparticles push each other and are trapped stably at two separated positions. Also, the inter-distance between them can be tuned precisely by changing the relative power of the two modes. This provides a potential method to control the interactions between two nano-objects via optically tuning the separation between them, and may have applications in various related disciplinary.