Orbital motion from optical spin: the extraordinary momentum of circularly polarized light beams

0494376 - ÚPT 2019 RIV CZ eng C - Conference Paper (international conference)
Svak, Vojtěch - Brzobohatý, Oto - Šiler, Martin - Jákl, Petr - Zemánek, Pavel - Simpson, Stephen Hugh
Orbital motion from optical spin: the extraordinary momentum of circularly polarized light beams.
Recent Trends in Charged Particle Optics and Surface Physics Instrumentation. Proceedings of the 16th International Seminar. Brno: Institute of Scientific Instruments The Czech Academy of Sciences, 2018, s. 78-79. ISBN 978-80-87441-23-7.
[Recent Trends in Charged Particle Optics and Surface Physics Instrumentation. Skalský dvůr (CZ), 04.06.2018-08.06.2018]
R&D Projects: GA ČR GB14-36681G; GA MŠMT(CZ) LO1212; GA MŠMT ED0017/01/01
Institutional support: RVO:68081731
Keywords : optical trapping * optical levitation * counter-propagating beams * optical spin
OECD category: Optics (including laser optics and quantum optics)

We provide a vivid demonstration of the mechanical effect of transverse spin momentum in an
optical beam in free space. This component of the Poynting momentum was previously thought
to be virtual, and unmeasurable. Here, its effect is revealed in the inertial motion of a probe
particle in a circularly polarized Gaussian trap, in vacuum. Transverse spin forces combine with
thermal fluctuations to induce a striking range of non-equilibrium phenomena. With increasing
beam power we observe (i) growing departures from energy equipartition, (ii) the formation of
coherent, thermally excited orbits and, ultimately, (iii) the ejection of the particle from the trap.
Our results complement and corroborate recent measurements of spin momentum in evanescent
waves, and extend them to a new geometry, in free space. In doing so, we exhibit fundamental,
generic features of the mechanical interaction of circularly polarized light with matter. The work
also shows how observations of the under-damped motion of probe particles can provide detailed
information about the nature and morphology of momentum flows in arbitrarily structured light
fields as well as providing a test bed for elementary non-equilibrium statistical mechanics.
Permanent Link: http://hdl.handle.net/11104/0287634