One usually considers imaging through the use of a lens. This approach has certain limitations, like a transfer function restricting the highest spatial frequencies that it can transmit combined with some aberrations. The k parameter we have discussed throughout the book is a vector whose projection onto a plane, such as an image plane, has a certain period or spatial frequency that contributes to defining detail in an image. Higher spatial frequencies contributing to an image usually means higher spatial resolution, i.e., more detail. The excitement generated by the negative-index metamaterial described in Chapter 6 arose from the suggestion that it might permit all k values generated by an object to be transferred to the image plane, thereby creating a ‘perfect’ image. The idea of having nanometer resolution using, for example, visible light with a 500-nm wavelength, would revolutionize imaging systems and have a huge impact in many areas of research and inspection. Moreover, the negative-index lens could be easy to make, having flat surfaces albeit associated with a very narrow depth of focus. This was also discussed in Chapter 6, and the limitations of using this idealized ‘perfect’ lens were reviewed. The question remains, How much improvement might be possible using metamaterial-based imaging systems? Issues to do with bandwidth, since negative index requires some resonant behavior, and depth of focus, in order to see 3D details in an object, are worth considering in more detail.
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