Surface-wave interferometry on single subwavelength slit-groove structures fabricated on gold films

We apply the technique of far-field interferometry to measure the properties of surface waves generated by two-dimensional (2D) single subwavelength slit-groove structures on gold films. The effective surface index of refraction nsurf measured for the surface wave propagating over a distance of more than 12 μm is determined to be nsurf = 1.016±0.004, to within experimental uncertainty close to the expected bound surface plasmon-polariton (SPP) value for a Au/Air interface of n spp = 1.018. We compare these measurements to finite-difference-time-domain (FDTD) numerical simulations of the optical field transmission through these devices. We find excellent agreement between the measurements and the simulations for nsurf. The measurements also show that the surface wave propagation parameter ksurf exhibits transient behavior close to the slit, evolving smoothly from greater values asymptotically toward k spp over the first 2-3 μm of slit-groove distance xsg. This behavior is confirmed by the FDTD simulations.