Fabry-Perot -like resonant transmission of microwave radiation through a single subwavelength slit in a thick aluminum plate is quantified for a range of slit widths. Surprisingly, and in contrast to previous studies [e.g., Y. Takakura, Phys. Rev. Lett. 86, 5601 (2001)], the resonant frequency exhibits a maximum as a function of slit width, decreasing as the slit width is reduced to less than 2% of the incident wavelength. This result accords with a new model based on coupled surface plasmon theory taking into account the finite conductivity, and hence permittivity, of the metal. This is contrary to a common assumption that metals can be treated as infinitely conducting in this regime.

It has recently been shown that the structured surface of a perfect conductor can support surfaceplasmon-like modes [Pendry et al., Science 305, 847 (2004)]. Such structures have a thickness of at least the order of the wavelength. Here, using microwave wavelength radiation incident beyond the critical angle of a wax prism, we quantify the surface-plasmon-like dispersion for a metamaterial surface with a thickness very much smaller than the incident wavelength.

Diffraction gratings are elementary tools for much of optics and spectroscopy. Here, at microwave frequencies, we provide a new perspective on these fundamental structures. A transmission diffraction grating is presented that has diffracted beams emanating from one surface only. It can thus function either as a transmission grating with no reflected orders ͑other than zero͒ or, in the reverse configuration, as a partially transmitting structure with diffracted orders in reflection only.

An array of subwavelength slits in a metallic substrate supports a series of Fabry-Perot-like resonances, where each harmonic results in a transmission peak. Addition of extra slits per period yields a compound grating with a structure factor associated with the basis. In this study each repeat period is comprised of a central slit flanked by a pair of narrower slits. It supports three resonances for every Fabry-Perot-like solution. New and useful insight into this phenomenon is gained by describing each of the modes in terms of the band structure of diffractively coupled surface waves.

We demonstrate optical control over the transmission of terahertz (THz) radiation through a single subwavelength slit in an otherwise opaque silicon wafer. The addition of periodic corrugation on each side of the wafer allows coupling to surface plasmon polaritons, so that light not impinging directly on the slit can contribute to the transmission. A significant enhancement of the THz transmission can be achieved through control of the surface wave propagation length by excitation at optical wavelengths. The observed transmission increase is in distinct contrast to the reduction reported for photoexcitation of arrays of holes in semiconductors. DOI: 10.1103/PhysRevLett.100.123901 PACS numbers: 42.79.Ag, 42.25.Fx, 73.20.Mf, 78.47.ÿp Stimulated by the seminal work of Ebbesen and coworkers [1], there is renewed interest in the optical properties of subwavelength slits in conductors (see Refs. [2,3] and references therein). A subwavelength slit in a conducting slab is known to support Fabry-Perot-like modes for light polarized perpendicular to the slit [4], giving rise to high transmission when the slab thickness is approximately equal to an integer number of half wavelengths. In addition to Fabry-Perot modes, electromagnetic surface waves (surface plasmons at visible frequencies [5]) also play a key role in determining the transmission of a single slit, in particular, in the presence of ordered surface corrugation at the entrance and exit interfaces. First reported at optical frequencies [2,6], a slit or hole can be made more transmissive by patterning the entrance and/or exit interfaces of the aperture. Similar effects have subsequently been demonstrated at microwave [7,8] and terahertz (THz) frequencies [9,10]. The transmission enhancement has been attributed to diffractive coupling of incident light to surface waves, defined by wave vectors parallel to the entrance and exit interfaces, allowing light that does not directly impinge upon the aperture to contribute to transmission. However, due to the different mechanisms which can give rise to peaks in transmission spectra for such structures [2], it is often difficult to differentiate Fabry-Perottype transmission features from effects due to surface waves.Here, we are able to modulate the low frequency, THz transmission of a semiconductor structure consisting of a slit in a silicon wafer surrounded by periodic corrugations by optically modifying the propagation lengths of surface waves at the wafer interfaces. This allows us to directly differentiate transmission resonances due to Fabry-Perot modes and surface wave excitation. In the THz frequency range (0.2 -2 THz), all-optical reduction of THz transmission has been demonstrated for several structures [11][12][13][14][15].Here, we show how all-optical enhancement of THz surface modes can increase THz transmission of a resonant structure, with enhancements approaching a factor of 3.The propagation length L of a surface wave propagating at the flat interface of a conductor and vacuum can vary over orders of ma...