18 October 2004 Colloidal crystallization induced by optical gradient forces exerted by optical tweezers
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Abstract
Optical tweezers were used to crystallize colloidal dispersions without manipulating colloids on a single particle level. Using "optical gradient" or "high-frequency dielectrophoretic" forces, we demonstrate control over local particle concentration. This control can be used to induce crystallization and melting in two- and three-dimensional colloidal dispersions using single beam gradient optical tweezers. In our setup, two microscope objectives (one above and one below the sample) allow independent three-dimensional manipulation and imaging of the structure formation inside the sample. We demonstrate crystallization near a wall for a range of particles sizes, refractive index contrasts and numerical apertures. In a colloidal mixture of tracer particles with a high refractive index core and low refractive index host spheres dispersed in a host refractive index matching solvent, control over the tracers can indirectly lead to controlled crystallization of the host particles.
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Dirk L. J. Vossen, Myrthe A. Plaisier, Alfons van Blaaderen, "Colloidal crystallization induced by optical gradient forces exerted by optical tweezers", Proc. SPIE 5514, Optical Trapping and Optical Micromanipulation, (18 October 2004); doi: 10.1117/12.558923; https://doi.org/10.1117/12.558923
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