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THE
controversy is over. After years of argument, physicists have
shown you really can build materials that will bend light the
opposite way from normal, reversing the way refraction usually
works. But whether or not such materials can fulfil the
prediction that they will act as "perfect lenses", capable of
focusing features smaller than the wavelength of light, is
still up for debate.
When light
enters or leaves a transparent material such as glass at an
angle, the rays get refracted, or bent. The light always bends
the same way. But in 1968, theorist Victor Veselago at the
Lebedev Physics Institute in Moscow speculated that it might
be possible to build a material that would bend light the
opposite way.
He was
thinking of the electric and magnetic fields of a ray of
light. The planes of these fields are normally perpendicular
to each other and to the direction in which the light is
moving. But Veselago calculated that if you could flip the
planes of the two fields, light would bend the opposite way,
and you would have a "left-handed" material.
Years later,
it fell to theorist John Pendry of Imperial College, London,
to work out how you might do that. He predicted in 1996 that
an array of thin parallel wires would reverse light's electric
field, while an array of copper rings should reverse the
magnetic field. The same would be true for any electromagnetic
radiation. Sure enough researchers who tested out the device
with microwaves said it bent them in the opposite direction to
normal (New
Scientist, 14 April 2001, p 35). But last year the
idea came under attack from groups who claimed that there were
problems with Pendry's theory and who argued that the
experimental results could have been misinterpreted (New
Scientist, 18 May 2002, p 11).
Now two other
groups have resolved the debate. Andrew Houck from Harvard and
his colleagues from MIT built a prism made of interlocking
fibreglass strips patterned with copper wires and rings and
fired a beam of microwaves at it (see
Graphic). When they measured the electric field inside and
outside the prism, they found the direction in which the beam
was refracted had flipped. Patanjali Parimi and colleagues at
Northeastern University in Boston saw similar effects after
firing a beam of microwaves at an array of copper rods.
The results
convinced other physicists at the meeting. "Contouring
electromagnetic fields in this way is very powerful," says
Clifford Krowne of the Naval Research Laboratory in Washington
DC. He believes left-handed materials could eventually be used
to build new components for optical telecommunications
equipment.
But the
prospects for making a perfect lens are less certain. In 2000,
Pendry predicted that a lens made of a left-handed material
should create images far sharper than usual. In a conventional
lens, "evanescent" waves carrying the finest details of an
image die off rapidly. But in a flat slab of left-handed
material, Pendry said these waves should get amplified and
focused into a "perfect" image.
Houck's team
followed microwaves spreading out from a tiny antenna as they
hit a flat slab of their left-handed material. The slab
focused the microwaves, but the image was much more blurred
than Pendry had predicted. Some researchers argue that a
perfect lens is impossible, but Pendry says the latest result
just means more work is needed. "Producing a near-perfect
image requires even more perfect materials," he says.
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