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A Bright Future for Subwavelength Light Sources

Generating tiny points of light for such things as storing data on optical disks is aided by a new theory involving evanescent waves

Tineke Thio

Figure 7. The new model invokes Click to Enlarge Image

The amount of data you can burn on a compact disk or DVD hinges, fundamentally, on the spot size of each data bit. Recording devices that rely on a focusing lens are restricted by the physical diffraction limit, but very small spot sizes can alternatively be made by passing the light through a tiny hole.  The roadblock is that holes that are much smaller than a wavelength in size typically do not allow much light to go through. Surprisingly, when the area surrounding the hole has surface corrugations, the power throughput of even very small holes can be enhanced considerably, to the point that it is useful for data recording.  Although she was once a staunch supporter of the idea that a phenomenon called surface-plasmon resonance accounted for this effect, the author has recently come to champion an entirely different explanation: the diffraction and interference of evanescent waves.


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