Rayleigh scattering of surface plasmons by sub-wavelength holes.

We study the scattering of surface plasmons from sub-wavelength holes and find that it exhibits a stronger wavelength dependence than the traditional λ(-4) scaling found for Rayleigh scattering of light from small particles. This experimental observation is consistent with recent theoretical work and linked to the two-dimensional nature of the surface plasmon and the wavelength dependence of its spatial extent in the third dimension. The scattering cross sections are obtained with a frequency-correlation technique, which compares intensity speckle patterns observed behind various random structures of holes and recorded at different wavelengths. This powerful technique even allows us to distinguish between scattering of surface plasmons into photons and scattering into other surface plasmons.

Surface plasmon dispersion in metal hole array lasers.

We experimentally study surface plasmon lasing in a series of metal hole arrays on a gold-semiconductor interface. The sub-wavelength holes are arranged in square arrays of which we systematically vary the lattice constant and hole size. The semiconductor medium is optically pumped and operates at telecom wavelengths (λ ~ 1.5 µm). For all 9 studied arrays, we observe surface plasmon (SP) lasing close to normal incidence, where different lasers operate in different plasmonic bands and at different wavelengths. Angle- and frequency-resolved measurements of the spontaneous emission visualizes these bands over the relevant (ω, k||) range. The observed bands are accurately described by a simple coupled-wave model, which enables us to quantify the backwards and right-angle scattering of SPs at the holes in the metal film.

Transmission processes in random patterns of subwavelength holes.

The optical transmission of random patterns of holes is believed to depend on the transmission of the independent holes only. By comparing the transmission spectra of random patterns with different densities, we show that the quasi-cylindrical wave plays an important role in the transmission of samples with large hole densities. Furthermore, we report on a speckle pattern seen in the transmission of these arrays. By studying the degree of depolarization in this speckle pattern, as a function of hole density, we are able to quantify the role of surface plasmons to the transmission.