Polarimetry studies on birefringent materials in optical tweezers

Catherine M. Herne; Faye E. Lyons; Enrique J. Galvez; Akza Sam

doi:10.1117/12.2567547

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20 August 2020 Polarimetry studies on birefringent materials in optical tweezers

Catherine M. Herne, Faye E. Lyons, Enrique J. Galvez, Akza Sam

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Proceedings Volume 11463, Optical Trapping and Optical Micromanipulation XVII; 1146312 (2020) https://doi.org/10.1117/12.2567547
Event: SPIE Nanoscience + Engineering, 2020, Online Only

Abstract

Transfer of spin angular momentum to birefringent materials is widely used in optical tweezers because of the vast array of applications and the ease with which it is generated. With circularly or elliptically polarized light, spin angular momentum is imparted to internally birefringent materials and objects with shape birefringence. In this work, we use polarimetry to spatially map the change in angular momentum of light traveling through birefringent objects. By directly measuring the change in polarization of light passing through materials, we can infer the transferred torque. Our objects are trapped with a linearly polarized beam at 660 nm and polarimetry is performed using a counter-propagating low-power probe beam at 633 nm. We measure six output polarizations each for a range of different input polarizations of the probe to form a polarization map. Using this technique we perform polarimetry on rhombohedral calcite crystals trapped in two distinct orientations, one face up with one side normal to the probe beam, and one corner up with the optic axis running parallel to the beam axis. The polarization changes significantly where the probe beam travels through an edge or corner of the crystal and is uniform across crystal faces. We show the differences in the polarimetry measurements between these orientations to fully understand the generated torque.

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Catherine M. Herne, Faye E. Lyons, Enrique J. Galvez, and Akza Sam "Polarimetry studies on birefringent materials in optical tweezers", Proc. SPIE 11463, Optical Trapping and Optical Micromanipulation XVII, 1146312 (20 August 2020); https://doi.org/10.1117/12.2567547

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