Twisted plasmons and chiral light

Coupling of light to surface plasmons (SP) – collective oscillations of the free charges at metal surface – is a strongly polarization selective process. In particular, only transverse magnetic polarization (magnetic field out of plane of incidence) can induce surface waves1. Nevertheless, when circular polarization is used for SP excitation, the resulting near-field distribution may be surprising. In this talk I will discuss an unusual dissymmetry observed in the plasmonic field distribution excited from a straight slit by an incident beam whose polarization is slightly tilted or elliptical. This phenomenon arises due to plasmonic spin-orbit interaction and is analyzed in terms of a “weak measurement” 2. 

It was shown that circular/spiral plasmonic structures can excite SP field carrying an orbital angular momentum (AM)3. However, plasmons are evanescent waves, propagating in the surface plane; therefore the AM flux of this mode is vanishing out of the surface. Here I show that a plasmonic wave can transfer AM along the surface of a subwavelength-thick metal membrane, guide it through an aperture to the back side of the membrane, and scatter it to light4. Through the investigation of this process we discover some intriguing AM selection rules determined by the aperture. Finally, the reduced dimensionality imposed by light-SP coupling allows generation of high-AM light beams by ultra-thin plasmonic elements.

  

References

[1] W. L. Barnes, A. Dereux, and T. W. Ebbesen, Nature 424, 824 (2003). 

[2] Y. Gorodetski, A. Niv, V. Kleiner, and E. Hasman, Phys. Rev. Lett. 101, 043903 (2008).

[3] Y. Gorodetski, A. Niv, V. Kleiner, and E. Hasman, Phys. Rev. Lett. 101, 043903 (2008).

[4] Y. Gorodetski, C. Genet, and T. W. Ebbesen, “Generating far-field orbital angular momentum from near filed optical chirality”, submitted to Phys. Rev. Lett. (2012).