Optically bound matter in a tractor beam

0451056 - ÚPT 2016 DE eng A - Abstract
Chvátal, Lukáš - Brzobohatý, Oto - Jákl, Petr - Zemánek, Pavel
Optically bound matter in a tractor beam.
Invitation and Programm 116th Annual Meeting of the DGaO. Erlangen: DGaO, 2015. s. 130.
[Annual Meeting of the DGaO /116./. 26.05.2015-29.05.2015, Brno]
Institutional support: RVO:68081731
Keywords : theoretical foundations * diffraction theory * micro optics
Subject RIV: BH - Optics, Masers, Lasers

In a `tractor beam’ a particle may experience an optical recoil force directed against the total field momentum. This effect occures either with isolated particles, or mutiple-particle structures spontaneusly formed due to secondary light scattering (`optical binding’). We investigate conditions yielding the `negative’ force for the simplest stucture, a pair of identical spheres, using numerical simulations based on the exact theory of multiple particle scattering and low-Reynolds-number hydrodynamics, To model the tractor beam in our calculations, we use a wide Gaussian beam counter-reflected at a small angle, thus forming a standing wave. In such beam the pairs end up with their centers moving uniformly, separated in space roughly by an integer number of wavelenghts, while spanning none or several fringes. We show that, for a large interval or sphere radii and their specific alignment, the tractoring can be provoked by adjusting the beam angle of incidence and/or its polarisation. In addition, we find pairs which move even faster than a single sphere in its optimal beam settings.
Permanent Link: http://hdl.handle.net/11104/0252295