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| Optical diagram of a single-interface Veselago lens. Image quoted from Yee Sin Ang et al., "Retro reflection of electrons at the interface of bilayer graphene and superconductor." |
I just learned of the Veselago lens, an imaging application of negative-one refractive index. The diagram above shows the simplest case, a single refractive index interface producing a real image: in fact, every object in ni will have a real image in -ni, and vice-versa. Uses of the Veselago lens (typically with two interfaces, as shown below) are being actively investigated by nano-materials scientists interested in genuinely propagating waves in a negative index medium. As we have seen, such is not necessary in solar power optics, if the divergence pattern has the right symmetry, a Fresnel mirror with its facets tilted 90° has optics identical to an ni/-ni interface.
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| Optical diagram of a two-interface Veselago lens. Image quoted from Lukas Novotny, "Principles of Nano-Optics." |
It is helpful to look at the Veselago lens from all four perspectives: retroflection, transmission, reflection, and transflection. If a room has a retro-reflective plane instead of a window, light will be returned directly back to each object in the room, forming a real image that happens to coincide in every case with the object itself, and thus has the same handedness. If there is indeed a transmissive plane where the window should be, an observer on the outside perceives a virtual image that happens to coincide in every case with the object itself, and thus has the same handedness. If there is a mirror (reflective plane) where the window should be, there is virtual image of the room (turned inside-out) in the space outside, and thus handedness is reversed. If there is a transflective plane (or equivalently, the ni/-ni interface of a Veselago lens) there is a real image of the room (turned inside-out) in the space outside, and thus handedness is reversed.
