Published in Physics World, 1 May 2012
Once thought to offer imaging at unlimited resolution beyond that permitted by diffraction, superlenses never quite worked in practice. Now, physicists have a host of other ideas to make perfect images, but can these concepts succeed where superlenses failed? Jon Cartwright reports
Ernst Abbe, one of the 19th-century pioneers of modern optics, has a concrete memorial sitting in the leafy grounds of the Friedrich Schiller University of Jena, Germany, engraved with a formula. Put simply, it describes a fundamental limit of all lenses: they cannot see everything. No matter how finely you grind and polish a lens, diffraction – the natural spreading of light waves – will always blur the smallest details.
Of course, theories should never be set in stone. At the turn of this century, physicists began to explore “superlenses” that could see past Abbe’s diffraction limit – that is, they could see features smaller than about half a wavelength of the light being used. Based on thin slabs of metal, these superlenses could bend light in unheard-of ways, counteracting diffraction so that an object’s features could be resolved into a perfect image. But there were problems: the lenses only worked if they were placed right next to an object and, even then, they were so lossy that their images were next to useless. Superlenses were not so super after all.
For many, that was a great shame. Biologists had been looking forward to imaging the tiniest parts of organisms in real time, which is almost impossible with current microscopy techniques. Perfect imaging could also have rebooted the computer-chip industry, allowing circuits and components to be etched smaller and more complex than before. Although other techniques exist that can see features smaller than half a wavelength – near-field scanning optical microscopy is one – they produce images by scanning a surface, which takes time. Only perfect imaging promised the ability to image objects at any resolution in a single snapshot.
Given the poor results of superlenses, some physicists have tried rehashing the blueprint in the hope that it can still offer practical applications. Others, however, have ditched the concept altogether, instead trying completely different approaches. These new approaches are in their nascent stages – most have not actually imaged anything, but only resolved point sources. Still, they are under high expectations, and could allow us to see more clearly than ever before. […]
For the rest of this article, please contact Jon Cartwright for a pdf.