2020/03/09 by Sumeet Kumar, M. Gunaseelan, Kumar, Sumeet +13 · 1 citation
Physics and Astronomy · Engineering · #Orbital Angular Momentum in Optics #Microfluidic and Bio-sensing Technologies
paper · pdf · doi:10.48550/arxiv.2003.06231
3D pitch rotation of microparticles and cells assumes importance in a wide\nvariety of applications in biology, physics, chemistry and medicine.\nApplications such as cell imaging and injection benefit from pitch-rotational\nmanipulation. Generation of such motion in single beam optical tweezers has\nremained elusive due to complicacies of generating high enough ellipticity\nperpendicular to the direction of propagation. Further, trapping an extended\nobject at two locations can only generate partial pitch motion by moving one of\nthe foci in the axial direction. Here, we use hexagonal-shaped upconverting\nparticles and single cells trapped close to a gold-coated glass cover slip in a\nsample chamber to generate complete 360 degree and continuous pitch motion even\nwith a single optical tweezers beam. The tweezers beam passing through the gold\nsurface is partially absorbed and generates a hot-spot to produce circulatory\nconvective flows in the vicinity which rotates the objects. The rotation rate\ncan be controlled by the intensity of the laser light and the thickness of the\ngold layer. Thus such a simple configuration can turn the particle in the pitch\nsense. The circulatory flows in this technique have a diameter of about 5\n\μm which is smaller than those reported using acousto-fluidic techniques.\n