Scientists playing with polymers and new dye materials at the University of Buffalo reckon they have perfected a technique for creating multi-layer compact disks that would be able to store 1,000 times more data than today’s disks – that means 650Gb, or enough capacity for 69 full length movies on one disk. When the infra-red laser reaches the end of the top track, it refocuses on the next one down, and so on through the disk. The technology, called two-photon absorption, uses the fact that a molecule can absorbs two photons of light simultaneously if the light beam has enough intensity. The team developed dyes with strong two-photon absorption and the ability to fluoresce intensely and laid them on transparent plastic films – the layers are just one micron thick, so that a 550-layer disk need be no more than 1mm thick. The absorption of light causes the material at the focal point to change properties, such as its color or fluorescence emission – providing the two states needed for binary storage. To find a new layer, the focal point simply needs to be changed, because two-photon absorption occurs only at the focal point. By using lasers of different intensities, the disks can be write-once or rewritable.
