Abstract
We demonstrate optical trapping and orientational control over colloidal particles having complex shapes in an anisotropic host fluid using a dynamic holographic optical tweezers system. Interactions between a colloidal particle and the toroidal intensity distributions of focused Laguerre-Gaussian beams allow for stable optical tweezing and provide a tunable tilt of the particle out of the focal plane. Use of an aligned nematic liquid crystal as the host fluid suppresses rotations about the optical axis arising from angular momentum transfer from the beam and effectively defines a rotational axis for the colloid within the trap.
Highlights
Laser tweezers [1] have provided an unprecedented level of control over fluid-borne particles, leading to experiments that have probed the intricate stepping of molecular motors [2], interparticle interactions [3], and colloidal assembly [4]
We demonstrate optical trapping and orientational control over colloidal particles having complex shapes in an anisotropic host fluid using a dynamic holographic optical tweezers system
Use of an aligned nematic liquid crystal as the host fluid suppresses rotations about the optical axis arising from angular momentum transfer from the beam and effectively defines a rotational axis for the colloid within the trap
Summary
Laser tweezers [1] have provided an unprecedented level of control over fluid-borne particles, leading to experiments that have probed the intricate stepping of molecular motors [2], interparticle interactions [3], and colloidal assembly [4]. We demonstrate that dielectric colloids having complex shapes, such as triangular and square-shaped platelets, suspended in an aligned nematic liquid crystal (NLC) can be stably trapped, oriented, and rotated about a predetermined axis that is orthogonal to the trapping laser beam's axis. We achieve this using a single Laguerre-Gaussian laser beam holographically generated by means of a spatial light modulator. Elastic repulsion between the particles and the bounding substrates provides a levitating force that overcomes gravity and suspends them in the NLC bulk, allowing for controlled holographic optical tweezing [25,26] experiments using colloids suspended away from both the top and bottom walls
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