Imagine a medium that reverses every notion you had about the electromagnetic (EM) behavior of materials. The index of refraction is negative so that light, for example, bends the ‘wrong way’ when it enters the medium from a vacuum. A flat plate of the medium could focus light instead of dispersing it. A light source located behind the plate would appear to be in front of it (Fig. 1). Because permittivity and permeability — the main determinants of a material’s response to EM energy — are both negative, EM waves appear to transmit energy one way while undulating the other. And the familiar right-hand rule for EM visualization becomes a left-hand rule.Among other strange consequences, the Doppler effect is reversed: a passing EM source would be characterized by falling then rising frequency rather than the other way around, while light from a source coming towards you would be reddened instead of blue-shifted. The Cerenkov effect is similarly reversed, with charged particles passing though a medium emitting light in a cone behind the particle rather than in front. Evanescent waves, with extremely short wavelengths that decay rapidly and never really escape the surface of a normal material, would actually grow in our topsy-turvy medium. In optics, therefore, these waves — less than the wavelength of light and carrying the finest details of an optical image — could be focused along with the normally propagating waves.

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DOI: 10.1016/S1369-7021(03)00128-7