April 24, 2008

A simple-to-make "superlens" can focus 10 times better than diffraction limit, microwaves so far, next 19-38 nm for visible light

A simple-to-make "superlens" can focus 10 times more sharply than a conventional lens. It could shrink the size of features on computer chips, or help power gadgets without wires. No matter how powerful a conventional lens, it cannot focus light down to more than about half its wavelength, the "diffraction limit". So far they have made it work with microwaves. Microwaves are electromagnetic waves with wavelengths ranging from 1 mm to 300 mm. So microwaves can be focused to 50 microns to 15 mm. The theoretical foundation of the new experimental work was described in 2007. [Near-field Focusing Plates and Their Design] Making capacitors of different sizes would allow the lens to focus other frequencies, including visible and infrared light, says Grbic. If they could make it work with far ultraviolet they could focus to 6 nanometers and extreme ultraviolet to 0.5-1 nanometers.

Grbic and colleagues have a variety of uses for their new lenses planned, including focusing light into smaller spots during photolithography to etch smaller features onto computer chips. The lenses could also help refine a technique to transfer power wirelessly developed in 2006. The new lenses could create more energy-dense beams of the electromagnetic waves used to transfer power, Grbic says. Nader Engheta of the University of Pennsylvania in Philadelphia, US, agrees, saying the new design has "exciting potential." But the more complex metamaterial lenses will likely be more applicable to more diverse applications, he adds.

Visible light has wavelengths of 380 to 750 nm. Half of those wavelengths is 190 to 375 nanometers. Ten times better is 19-38 nanometers.

The new lens is a 127-micrometer-thick plate of teflon and ceramic with a copper topping. "The beauty of these is that they're planar," Grbic says, "they're easy to fabricate." The lenses can be made through a single step of photolithography, the process used to etch computer chips.

Anthony Grbic, Lei Jiang and Roberto Merlin at the University of Michigan in Ann Arbor, US, have now successfully made a much simpler design, first theorised last year.

By selectively etching away the copper, Grbic and colleagues created many capacitors sandwiched together. Capacitors are typically used in electronics for storing electric charge for short periods.

In the lens, the capacitors instead interact directly with electromagnetic waves like light. This sets up currents in the capacitors that focus the waves passing through the lens into a point 20 times smaller than their wavelength. That is 10 times tighter than a conventional lens can achieve, hampered by the diffraction limit.

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