Our experiments have used arrayed traps in the near field of a photonic crystal to selectively capture nanoparticles by size. The photonic crystal is designed to support a guided resonance mode, and the incident laser is tuned to the resonance wavelength. Each hole of the photonic crystal acts as a trapping site.
In this work, we use simulations of particle dynamics to determine the optimal experimental conditions for size selection. We include the effects of optical forces, fluid flow, and Brownian motion and explicitly track the trajectories of particles near an array of trapping sites. We study the effects of varying chamber height, flow rate, and particle concentration on size selectivity and trapping yield. We further present photonic crystal designs for selectively trapping smaller or larger particles out of mixed-particle solutions.
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