Surface-plasmon enhanced optical transmission through subwavelength apertures in metal films

Summary form only given. The optical transmission through an aperture in an optically thick metal film is expected to have extremely low transmission efficiency T if the aperture diameter d is much smaller than the wavelength /spl lambda/ of the incident radiation, with T/spl sim/(d//spl lambda/)/sup 1/4/. Surprisingly, the transmission through an array of such subwavelength holes exceeds that expected by up to several orders of magnitude, and can even be larger than f, the fractional area occupied by the holes. In this work we present direct evidence for the crucial role played by the surface plasmons. We have constructed square arrays of subwavelength apertures (750nm) in free-standing metal membranes of thickness 220 nm. The transmission spectrum of a bare Ni membrane shows maxima at wavelengths expected for the surface plasmons for this structure.