ONE of the most intriguing ideas in optics - that a "super-lens" can focus features that are much smaller than the wavelength of light illuminating the object - has been independently verified by two experiments.

The key to a super-lens lies in the so-called "evanescent" waves that objects emit along with visible light. Conventional optical devices are unable to focus these waves because they decay rapidly as they pass through normal lenses. Five years ago, John Pendry of Imperial College London predicted that materials that refract light the opposite way to ordinary materials could focus these evanescent waves.

Now, two teams have shown that extremely thin silver foil has a negative refractive index and so acts as a super-lens. Xiang Zhang of the University of California in Berkeley used a layer of silver 35 nanometres thick to form 60-nanometre-wide images of nanowires - about one-sixth of the wavelength of the ultraviolet light illuminating the wires (Science, vol 308, p 534). Richard Blaikie of the University of Canterbury in Christchurch, New Zealand, used a similar silver lens to focus features 70 nanometres wide (Optics Express, vol 13, p 2127).

The technique is of more than just theoretical interest. Such lenses can be used to fabricate microchips with much finer features than is possible with today's best optics, says David Smith of Duke University in Durham, North Carolina.