Towards optics: metals or dielectrics?

Until early 2005, all current demonstrations of these "left-handed" materials based on interlocking metal networks were in the microwave domain. For higher frequencies, the laws of scale (i.e. the size of the constituent objects is small compared with the wavelength) require miniaturization, which can reach the limits of electronic nanolithography for the smallest elements. What's more, the physical properties of thin-film metals (saturation effect of electron-induced resonances beyond the far infrared) limit the degrees of freedom offered by nanostructuring, mainly in terms of magnetic properties. Nevertheless, by working on pattern geometries and the metals used, the extension of negative refraction properties to several tens of terahertz...