Optical trapping serves as a powerful tool for the manipulation of matter on the nanoscale and ultra-precise measurement of weak forces. However, the applicability of these tools is limited by the available laser power and trap efficiency. We utilized the strong confinement of light in a slot-graphite photonic crystal to develop high-efficiency parallel trapping over a large area. The stiffness is several orders of magnitude higher than conventional optical tweezers and two orders of magnitude higher than our previously demonstrated on-chip, near field traps. We demonstrate the ability to trap both dielectric and metallic nanoparticles of sub-micron size. We find that the growth kinetics of nanoparticle arrays on the slot-graphite template depends on particle size. Smaller particles diffuse more, more readily occupying the available trap sites and inhibiting the trapping of larger particles. Smaller particles also sink more into the holes in the photonic crystal, resulting in stronger mechanical confinement and a deeper potential well. We use these differences to selectively trap one type of particle out of a binary colloidal mixture, creating an efficient optical sieve. This technique has rich potential in the fields of trace analysis, optical diagnostics, and enrichment and sorting of microscopic entities and molecules.
Aravind Krishnan, Michelle L. Povinelli, Shao-Hua Wu, and Ningfeng Huang, "Enhanced and preferential optical trapping in a slot-graphite photonic crystal
(Conference Presentation)," Proc. SPIE 9922, Optical Trapping and Optical Micromanipulation XIII, 99221Z (Presented at SPIE Nanoscience + Engineering: September 01, 2016; Published: 10 November 2016); https://doi.org/10.1117/12.2238966.5161456690001.
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