Synchronization of colloidal rotors through angular optical binding

0464941 - ÚPT 2017 RIV US eng J - Journal Article
Simpson, Stephen Hugh - Chvátal, Lukáš - Zemánek, Pavel
Synchronization of colloidal rotors through angular optical binding.
Physical Review A. Roč. 93, č. 2 (2016), 023842:1-12. ISSN 2469-9926. E-ISSN 2469-9934
R&D Projects: GA ČR GB14-36681G
Institutional support: RVO:68081731
Keywords : hydrodynamic properties * colloidal rotors * angular optical binding
Subject RIV: BH - Optics, Masers, Lasers
Impact factor: 2.925, year: 2016

A mechanism for the synchronization of driven colloidal rotors via optical coupling torques is presented and analyzed. Following our recent experiments [Brzobohaty et al., Opt. Express 23, 7273 (2015)], we consider a counterpropagating optical beam trap that carries spin angular momentum, but no net linear momentum, operating in an aqueous solvent. The angular momentum carried by the beams causes the continuous low-Reynolds-number rotation of spheroidal colloids. Due to multiple scattering, the optical torques experienced by these particles depend on their relative orientations, while the effect of hydrodynamic interaction is negligible. This results in frequency pulling, which causes weakly dissimilar spheroids to synchronize their rotation rates and lock their relative phases. The effect is qualitatively captured by a coupled dipole model and quantitatively reproduced by T -matrix calculations. For pairs of rotors, the relative torque Delta tau is shown to vary with relative phase Delta phi according to Delta tau approximate to A sin(2 Delta phi + delta) + B for constants A, B, delta, so the resulting motion is governed by the well-known Adler equation. We show that this behavior can be preserved for larger numbers of particles. The application of these phenomena to the inertial motion of particles in vacuum could provide a route to the sympathetic cooling of mesoscopic particles.
Permanent Link: http://hdl.handle.net/11104/0263679