Excitation of surface plasmon polaritons by nano-hole and 2-D active optics by nano-hole arrays.

摘要

The surface plasmon is a collective fluctuation of electric charge density in a metal-dielectric interface. The coupled modes of the radiative photons and the surface plasmons are called surface plasmon polaritons. The surface plasmon polariton is a longitudinal electromagnetic mode with a transverse magnetic field. The electromagnetic field induced by the surface plasmon polaritons is evanescent and nonradiative. Special surface structures are required to help match the momentum of a photon to that of a surface plasmon polariton.; This thesis demonstrates a method of launching surface plasmon polariton waves on a metal film surface utilizing subwavelength circular apertures, or nano-holes. The excited surface plasmon polariton wave is found having a dominant in plane dipole angular distribution along the direction of polarization. This could be seen by analyzing holographic images of the localized surface plasmon polariton wave around the nano-hole with a near-field scanning optical microscope. The holographic images directly display the amplitude, wave vector, and phase of the surface plasmon polariton wave. Light having different polarizations and incident at different angles effectively changes features of the stationary near-field pattern. A finite-difference time-domain computer simulation of the experiments reveals excellent agreement to the experiments and indicates that perturbations due to the probe are small and do not jeopardize the features in the near-field images.; Based on the results of a single nano-hole, several arrays of nano-holes were fabricated into the thin metal films to create desired two-dimensional optical elements for the surface plasmon polariton waves. The propagation of the surface plasmon polariton wave on metal strips having a subwavelength width is also investigated with the near-field scanning optical microscopy. The experiments show that the surface plasmon polariton waves are not diffraction limited and can propagate along paths narrower than their wavelength. These experimental results suggest a significant opportunity for novel applications and optical devices for surface plasmon polariton waves.