14 March 2005 Rotating optical tweezers
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Abstract
Several methods to rotate and align microscopic particles controllably have been developed. Control of the orientation of a trapped particle allows full three dimensional manipulation, whereas rotating particles are tools for the development of optically-driven micromachines. It has been shown that the orientation of an object in the laser trap depends on its birefringence as well as on its shape. The effect of shape is often referred to as form-birefringence. We report on the trapping, rotation, and in-situ growth of birefringent tetragonal lysozyme crystals in optical tweezers operating at a wavelength of 1064 nm. Variation of the temperature, pH and lysozyme concentration of the solution during growth was used to alter the size, as well as the length to width ratio of the crystals, and hence their orientation in the tweezers. Thus this system serves as a model to study the relative importance of birefringence versus form-birefringence for particle orientation. Crystals with the optical axis skewed or perpendicular to the trapping-beam axis could be rotated by changing the orientation of linearly polarized light. We observed spontaneous spinning of some asymmetric crystals in the presence of linearly polarized light, due to radiation pressure effects. Addition of protein to the solution in the tweezers permitted real-time observation of crystal growth.
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Wolfgang Singer, Timo A. Nieminen, Ursula Jane Gibson, Norman R. Heckenberg, Halina Rubinsztein-Dunlop, "Rotating optical tweezers", Proc. SPIE 5736, Nanomanipulation with Light, (14 March 2005); doi: 10.1117/12.590107; https://doi.org/10.1117/12.590107
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