Plasmonic coherent drive of an optical trap.

We demonstrate that optical trapping can be driven by delocalized surface plasmon modes resonantly excited within a standing wave trap. Dynamical modifications are shown to be determined by the near-field symmetry of the plasmonic modes with negligible thermal effect. With low trapping powers and polarization control, remarkable stiffness enhancements are recorded, the larger the smaller the particle. The results can be simply modeled accounting for a coherent interaction between the plasmon field and the Gaussian standing wave of the trap.

Mechanisms for extraordinary optical transmission through bull's eye structures.

We analyze both experimentally and theoretically the physical mechanisms that determine the optical transmission through deep sub-wavelength bull's eye structures (concentric annular grooves surrounding a circular hole). Our analysis focus on the transmission resonance as a function of the distance between the central hole and its nearest groove. We find that, for that resonance, each groove behaves almost independently, acting as an optical cavity that couples to incident radiation, and reflecting the surface plasmons radiated by the other side of the same cavity. It is the constructive contribution at the central hole of these standing waves emitted by independent grooves which ends up enhancing transmission. Also for each groove the coupling and reflection coefficients for surface plasmons are incorporated into a phenomenological Huygens-Fresnel model that gathers the main mechanisms to enhance transmission. Additionally, it is shown that the system presents a collective resonance in the electric field that does not lead to resonant transmission, because the fields radiated by the grooves do not interfere constructively at the central hole.

Holes with very acute angles: a new paradigm of extraordinary optical transmission through strongly localized modes.

It is shown that submicrometer holes with very acute angles present extraordinary optical transmission peaks associated to strongly localized modes. The positions of these peaks are: (i) strongly redshifted with respect to the peak position that could be expected if the considered hole were in a film made of perfect electric conductor, (ii) independent on the angle of incidence for a large range of angles and (iii) strongly dependent on the direction of the incident electric field. In addition, it is demonstrated that these properties are linked to the mechanisms leading to the existence of channel-plasmon-polaritons.

Optimization of bull's eye structures for transmission enhancement.

We present an exhaustive exploration of the parameter space defining the optical properties of a bull's eye structure, both experimentally and theoretically. By studying the resonance intensity variations associated with the different geometrical features, several parameters are seen to be interlinked and scale laws emerge. From the results it is possible to give a simple recipe to design a bull's eye structure with optimal transmission properties.