superlens

A superlens is an imaging device designed to surpass the diffraction limit of conventional lenses by managing evanescent waves, which carry sub-wavelength information but decay rapidly in usual optics. By restoring or transmitting these near-field components, a superlens can in principle form images with finer detail than the wavelength would normally allow.

The concept was popularized by John Pendry in 2000, who showed that a slab of material with negative refractive index could amplify evanescent waves and produce a perfect image in the limit of negligible loss. Realistic implementations use materials with negative permittivity or permeability or engineered metamaterials to enhance near-field components, rather than achieving an exact lossless, n = -1 medium.

Practical realizations focus on near-field interactions. Plasmonic metals such as silver or gold, thin metal-dielectric stacks, and other metamaterial structures have demonstrated sub-wavelength imaging in the near field, but are limited by absorption losses, restricted bandwidth, and the need for object–lens proximity on the order of tens to hundreds of nanometers.

Variants of the concept include the hyperlens, which employs anisotropic metamaterials to convert evanescent information into propagating waves for some far-field sub-wavelength imaging, and other wave systems such as acoustics and microwaves. Overall, the term encompasses both theoretical proposals and experimental demonstrations aimed at surpassing the diffraction limit, while practical devices face significant challenges related to loss, bandwidth, and fabrication.