Lenses that bring everything into focus
Scientists at the University of Michigan have developed a new lens device that will shrink huge light waves to pinpoints. The superlens looks like a plate and "is etched with a specific pattern. As the waves pass through the patterned lens, it is sculpted into different sizes and shapes. The lens does not refract, or bend the light waves -- which is how conventional lenses work -- but rather it reshapes the wave." This discovery could lead to CDs or DVDs holding 100 times more information than current ones.
The picture above shows "a color-coded plot of the electromagnetic field. The device, or plate, is at the left edge of the picture. Focusing is clearly seen at the horizontal axis value of seven." (Credit: Roberto Merlin) Here is a link to a larger version of this image.
Roberto Merlin , professor of physics at U-M, is working with assistant professor Anthony Grbic from the U-M College of Engineering to build the device.
Here is what Merlin said about this new superlens. "Materials respond differently to different wavelengths, and when using electromagnetic waves, one is usually limited by the length of the light wave, Merlin said. For example, the amount of information you can store on a CD is limited by the number of bits you can fit on the CD, and this is dictated by the length of the electromagnetic wave. The smaller the wavelength, the smaller the bit, which means more bits of data can be stored on the CD."
So he used mathematical models to developed a formula that removes the wavelength limitation. In "New Superlensing Technique Brings Everything into Focus," Scientific American gives additional details.
"This construction is a way to convert traveling waves into evanescent waves," says Roberto Merlin, a physicist at the University of Michigan at Ann Arbor and author of the study published today in the online journal Science Express. Unlike ordinary light waves (such as sunlight), which can travel forever, evanescent waves traverse only very short distances before dying out. Whereas most of the light shining on such a plate is reflected back, a portion of the light leaks out the other side in the form of evanescent waves.
If these waves, which have slipped through the different slits between the circles, can blend before disappearing, they form a single bright spot much smaller than the wavelength. The plate effectively acts like a "superlens", and the focal length or distance between the lens and the spot is nearly the same as that between the plate's bright center and dim edge; the size of the spot is fixed by the spacing between the circles.
This research work has been published online by Science Express under the name "Radiationless Electromagnetic Interference: Evanescent-Field Lenses and Perfect Focusing" (July 12, 2007). Here is a link to the abstract which ends with this. "Practical implementations of these plates hold promise for near-field data storage, noncontact sensing, imaging, and nanolithography applications."
Sources: University of Michigan news release, July 12, 2007, via EurekAlert!; Sourish Basu, Scientific American, July 12, 2007; and various websites
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