Surface plasmons in metal hole arrays have been studied extensively in the context of extraordinary optical transmission, but so far these arrays have not been studied as resonators for surface plasmon lasing at optical frequencies. We experimentally study a metal hole array with a semiconductor (InGaAs) gain layer placed in close (20 nm) proximity of the metal hole array. As a function of increasing pump power, we observe an intense and spectrally narrow peak, with a clear threshold. This laser emission is donut shaped and radially polarized. Three experimental observations support that the system shows surface plasmon lasing. First, the full wavelength dispersion of the observed resonances can be understood by using a single surface plasmon mode of the system. Second, the polarization of these resonances is as expected for surface plasmons. Third, the magnitude of the avoided crossing, which results from mode coupling at the holes, has a similar magnitude as found in simulations using surface plasmons.

We present an experimental and theoretical study of the optical transmission of a thin metal screen perforated by two subwavelength slits, separated by many optical wavelengths. The total intensity of the far-field double-slit pattern is shown to be reduced or enhanced as a function of the wavelength of the incident light beam. This modulation is attributed to an interference phenomenon at each of the slits, instead of at the detector. The interference arises as a consequence of the excitation of surface plasmons propagating from one slit to the other. DOI: 10.1103/PhysRevLett.94.053901 PACS numbers: 42.79.Dj, 73.20.Mf, 78.66.Bz Recently, there has been a surge of interest in the phenomenon of light transmission through subwavelength apertures in metal plates. This followed the observation by Ebbesen et al. [1] that the transmission through a twodimensional hole array can be much larger than predicted by conventional diffraction theory [2]. This discovery has rekindled the interest in a similar but simpler problem, viz., the transmission of a one-dimensional array of subwavelength slits in a metal film, i.e., of a metal grating [1,[3][4][5][6][7][8][9][10][11][12][13][14][15][16]. In many cases the enhanced transmission of hole or slit arrays has been explained in terms of the excitation of (coupled) surface plasmons on the metal film [3][4][5][6], an explanation that has recently been challenged [16]. It has been shown that, for slit arrays, Fabry-Pérot-type waveguide resonances can also give rise to a considerably enhanced transmission [5,7,9,10,12].In the present Letter we study an even more fundamental system than the metallic grating, namely, a thin metal layer perforated by just two parallel subwavelength slits. In contrast to the systems that have recently attracted so much attention, our slits are separated by many optical wavelengths. Thus we study the light transmission of a setup that lies at the heart of wave physics, namely, that of Thomas Young. We do, however, not focus on the wellknown interference pattern named after him, but on the angle-integrated power transmission coefficient of the perforated screen, i.e., the transmission integrated over many interference orders. We show that this transmission coefficient is strongly modulated as a function of the wavelength of the incident light for the case that that light is TMpolarized, i.e., with the electric field aligned perpendicular to the slits. In contrast, there is no such modulation when the incident light is TE-polarized, or when the ''wrong'' metal is chosen. All our observations can be explained in terms of a model involving the coherent transport of electromagnetic energy between the slits by surface plasmons.Our samples consist of a 200 nm thick gold film, evaporated on top of a 0.5 mm thick fused quartz substrate with a 10 nm thick titanium adhesion layer between the gold and the glass. In such a sample a two-slit pattern is written using a focussed ion beam, each slit being 50 m long and 0:2 m wide. The slits are separated by a dis...