91av

THERE’S a limit to how many movies you can get onto a DVD and how many
transistors onto a silicon chip—the wavelength of light. This is because
physicists use light to record bits of data or make tiny components, but have
been unable to focus light to a spot smaller than that light’s wavelength. But
now a British researcher says he can focus light to a spot hundreds of times
smaller than its wavelength using an entirely new sort of lens.

The traditional view of light is of oscillating electric and magnetic fields
propagating neatly through space. Conventional lenses focus light by shifting
the timing of the waves—their “phase”—and the precision of the focus
is limited by the light’s wavelength.

But very close to its source, light is much more complicated. In this region,
light also contains static electric and magnetic fields collectively known as
its “evanescent field”. The size of these stationary waves drops off extremely
rapidly as you move away from the source and they disappear after only a few
dozen nanometres, so physicists have usually ignored them.

But John Pendry of Imperial College, London, thinks the evanescent field
could be put to good use. He says that a novel type of lens can make an image of
the evanescent field that mirrors the original light source
(see Diagram). The
lens is not shaped like a conventional lens, but is a plain film roughly 40
nanometres thick of a material such as silver with a negative dielectric
constant—it bends the electric part of the field in the opposite way to
other materials.

On the near surface of the lens, electrons respond to the evanescent wave by
setting up an increasing electric potential in the silver. This potential
propagates through the film, increasing in amplitude as it goes, until at the
far surface it produces a new evanescent wave in what Pendry describes as a
“slingshot effect”. This new wave then decays to an image of the original
source.

Pendry says there is no theoretical limit to the precision with which the
near-field waves can be focused, so the image should be true to within
nanometres. “When I first did the calculations, I didn’t believe it,” he says.
“But now I’m calling it miraculous.”

“It is a very interesting idea and certainly correct,” says Sheldon Schultz
at the University of California, San Diego, who with David Smith has developed a
structure with a negative refractive index, bending light in the opposite
direction to normal materials (91av, 25 March, p 5). Pendry
says this material will be the perfect lens, able to focus the magnetic as well
as the electric part of the evanescent field.