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Light-Assisted, Templated Self Assembly Using Photonic Crystal Slabs

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Technical Report

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University of Southern California Marina del Rey United States

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In this thesis we have successfully demonstrated the technique that we call light-assisted, templated self assembly. In the first demonstration we successfully trapped an array of 520 nm polystyrene particles above a square lattice.The number of particles trapped was well above 100, and could be increased by using a larger beam or a mode with a larger quality factor. The traps were characterized using standard techniques and were found to have stiffness values comparable to those reported elsewhere in the literature for single-particle traps. The system behaved as an array of non-interacting optical traps, with each trap positioned above the hole in each unit cell of the square lattice. Although other techniques exist for trapping arrays of particles, they typically require a spatial light modulator and fast scanning mirrors. Our technique requires just a simple, Gaussian input beam. Next we repeated the LATS technique but with metallic particles. Our expectation was that the technique would either work -- namely that we would trap an array of the metallic particles --or it would not work. Instead, we found an intermediate case involving the emergence of one-dimensional particle chains trapped in a two-dimensionally periodic potential due to the mode in the slab. The chains were observed to align in the direction opposite to the incident polarization of the beam. The particles in chains were self-stabilizing in the sense that these particles persisted much longer than other particles that were trapped in isolated positions. We explained these results by using a simplified model of the particle scattering in the absence of the slab. The system is best understood as a competition between particle-template and particle-particle interactions.

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  • Optics
  • Atomic and Molecular Physics and Spectroscopy

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