Enhanced Light Transmission through Subwavelength Holes
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Enhanced Light
Transmission through Subwavelength Holes José Dintinger, Aloyse Degiron, and Thomas W. Ebbesen
Abstract The transmission of light through a hole was thought to be very weak when all of the lateral dimensions of the hole were much smaller than the wavelength of the light. The discovery of enhanced transmission has changed this view, raising fundamental questions and leading to many practical applications ranging from photonics to chemical sensing. A key feature of the transmission process is the activation of surface plasmons. In this article, we review the present understanding of this phenomenon and illustrate its potential through several examples of applications in different fields. Keywords: apertures, light transmission, nanostructured metals, optics, subwavelength holes, surface plasmons.
Introduction Materials structured on the nanometer scale give rise to many interesting new properties and phenomena. These include optical effects, where the critical length scale is that of the wavelength of light (i.e., a few hundred nanometers). For instance, the interaction of light with nanostructured metals can give rise to hybrid surface waves known as surface plasmons1 (SPs), which have generated considerable interest in recent years for their potential applications in a variety of fields from biology to optoelectronics. A surface plasmon is essentially light trapped at a metal interface as a result of its interaction with the free electrons of the metal, giving rise to collective electronic oscillations. The interest in SPs lies in the fact that they provide a unique way of confining light at a metal–dielectric interface in a subwavelength volume, which in turn generates intense local electromagnetic fields, opening the way for miniaturized optical devices, photonic circuits, sensors, and so forth.2 For instance, the high local fields of SPs can be exploited to increase the efficiency of various effects such as second-harmonic generation (i.e., doubling the frequency of light), Raman scattering, and biological sensing.3–5 MRS BULLETIN • VOLUME 30 • MAY 2005
The rich potential of SPs has been further demonstrated with the discovery of enhanced optical transmission through subwavelength apertures in optically thick metal screens6 such as the one shown in Figure 1a. In this phenomenon, light is transmitted through subwavelength holes surrounded by periodic structures with an efficiency that is orders of magnitude greater than that predicted by classical theory. This is especially unexpected for holes with lateral dimensions smaller than half the wavelength, through which light cannot freely propagate (i.e., the aperture sustains no propagating mode). In this case, transmission is only possible via photon tunneling, a mechanism that is often highly inefficient.7,8 In contrast, the transmittance per hole in the enhanced transmission phenomenon can even exceed unity at certain wavelengths,6,9 because the whole corrugated surface acts like an antenna in the optical range. For example, Figure 1b shows the
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