Far-field imaging by a planar lens: Diffraction versus superresolution

We resolve the long-standing controversy regarding far-field imaging by a planar lens made of a left-handed medium and demonstrate theoretically that the far-field image has a fundamentally different origin depending on the relationship between losses inside the lens and the wavelength of the light, λ. At small enough λ, the image is always governed by diffraction theory, and the resolution is independent of the absorption if both Im ϵ⪡1 and Im μ⪡1. For any finite λ, however, a critical absorption exists below which the superresolution regime occurs, although this absorption is extremely low and can hardly be achieved. We demonstrate that the transition between the diffraction-limited and superresolution regimes is governed by a universal parameter combining absorption, wavelength, and lens thickness. Finally, we show that this parameter is related to the resonant excitation of surface plasma waves.