Negative optical torque on a microsphere in optical tweezers

Abstract

We show that the optical force field in optical tweezers with elliptically polarized beams has the opposite handedness for a wide range of particle sizes and for the most common configurations. Our method is based on the direct observation of the particle equilibrium position under the effect of a transverse Stokes drag force, and its rotation around the optical axis by the mechanical effect of the optical torque. We find overall agreement with theory, with no fitting, provided that astigmatism, which is characterized separately, is included in the theoretical description. Our work opens the way for characterization of the trapping parameters, such as the microsphere complex refractive index and the astigmatism of the optical system, from measurements of the microsphere rotation angle.

10 pages, 5 figures

References in corpus (10)

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Cited by in corpus (10)

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• Nonlinearity-induced optical torque
• Probing the optical chiral response of single nanoparticles with optical tweezers
• Tailoring bistability in optical tweezers with vortex beams and spherical aberration
• Radiation forces and torques in optics and acoustics
• Precise in situ radius measurement of individual optically trapped microspheres using negative optical torque exerted by focused vortex beams
• Optical Supertorque Induced by Mie-Resonant Modes
• Enantioselective manipulation of chiral nanoparticles using optical tweezers
• Gain-assisted optical tweezing of plasmonic and large refractive index microspheres
• Optical trapping with structured light