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 鈥減erfect lenses鈥�, 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 鈥渓eft-handed鈥� material.
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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鈥檚 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 (快猫短视频, 14 April 2001, p 35). But last year the idea came under attack from groups who claimed that there were problems with Pendry鈥檚 theory and who argued that the experimental results could have been misinterpreted (快猫短视频, 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. 鈥淐ontouring electromagnetic fields in this way is very powerful,鈥� 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, 鈥渆vanescent鈥� 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 鈥減erfect鈥� image.
Houck鈥檚 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. 鈥淧roducing a near-perfect image requires even more perfect materials,鈥� he says.
