Berlin 2014 – scientific programme

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Q: Fachverband Quantenoptik und Photonik

Q 30: Poster: Photonics, laser development and applications, ultrashort laser pulses, quantum effects

Q 30.83: Poster

Tuesday, March 18, 2014, 16:30–18:30, Spree-Palais

Negative azimuthal force of nanofiber-guided light on a particle — •Fam Le Kien and Arno Rauschenbeutel — VCQ, TU~Wien -- Atominstitut, Stadionallee 2, 1020 Wien, Austria

It is well known that radiation pressure due to the momentum flux in a light beam tends to push illuminated objects along the direction of propagation. Recent studies have shown that small particles can be pulled by so-called tractor light beams against the photon stream even when the beam intensity is uniform along the propagation axis. Such a pulling force occurs when the projection of the total incident photon momentum along the propagation direction is small and the forward scattering is dominant.

In this work, we study the Poynting vector and the force of the evanescent wave of a quasicircularly polarized guided light field in a nanofiber on a dielectric spherical particle. We show that the orbital parts of the axial and azimuthal components of the Poynting vector are always positive while the spin parts can be either positive or negative. The presence of the spin part of the axial Poynting vector component is related to the presence of the longitudinal component of the guided light field. It is the source of the negative axial Poynting vector obtained for high-contrast optical nanofibers. We find that, for appropriate values of the size parameter of the particle, the azimuthal component of the force is directed oppositely to the circulation direction of the energy flow around the nanofiber. The occurrence of such a negative azimuthal force indicates that the particle undergoes a negative torque.