A wavefront phase dislocation due to the scattering of surface plasmons from a topological defect is directly measured in the near-field by means of interference [1]. The dislocation strength is shown to be equal to the incident optical spin with analogy to the magnetic flux parameter in the Aharonov-Bohm effect [2].

  A circular nanoslit was used to excite an out-propagating plasmonic wavefront. We measured the scattered plasmonic-wave dislocation strength by its interference with an additional plasmonic reference wave. The dislocation strength was shown to be equal to the incident optical spin (polarization helicity) in a manner similar to the Aharonov-Bohm wavefunction dislocation strength being equal to the magnetic flux parameter. Moreover, we experimentally demonstrated that the surface plasmon-polariton wave dislocation is independent on the incident wavelength and the nanoslit diameter, therefore verifying the geometric nature of the phenomenon. This effect is attributed to the optical spin-orbit interaction – coupling of the intrinsic angular momentum - spin and the extrinsic (orbital/linear) momentum of the electromagnetic field [3]. Our experiment was analyzed using a rotating reference frame, which leads to a spin-dependent correction of the momentum term in the wave equation. The experiment and analysis presented in this letter elucidate the significance of the optical spin in the scattering of surface plasmon-polaritons from a topological defect and its connection to the plasmonic phase dislocation.

References:

1.              Y. Gorodetski, S. Nechayev, V. Kleiner, and E. Hasman, Phys. Rev. B 82, 125433 (2010).

2.              Y. Aharonov and D. Bohm, Phys. Rev. 115, 485 (1959).

3.              N. Dahan, Y. Gorodetski, K. Frischwasser, V. Kleiner, and E. Hasman, Phys. Rev. Lett. 105, 136402 (2010).

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