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Finding a Speed Limit to Writable Optical Discs


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While Flash memory drives have certainly caused a decline in the use of rewriteable optical discs, they are still used and being improved upon. The question some have for these media is just how fast data can be written to the discs. Researchers at Caltech believe they have discovered something that will fundamentally limit the speed one can write to these discs, but it could also lead to new memory systems with advanced properties.

Rewritable optical discs, both DVDs and BDs, use phase change materials that lasers are able act on. By transitioning the material in a spot from crystalline to amorphous, the optical properties change and a bit of data can be stored. The process is a bit more involved than that, and to study it the researchers first fired a femtosecond laser at the material, triggering the change, and then a beam of electrons. The electrons would arrive later and based on how they scatter the researchers could determine the new structure of material. What they discovered is a previously unknown intermediary step, and because this step takes time to complete, it puts a speed limit on the process. So, even with ever faster lasers, you can only write to an optical disc so quickly.

This discovery is not exclusively bad news though, as the information it has given us about the limits of phase-change materials could influence future memory technologies that also use them. The next step for the research though is to study the process of turning the amorphous structure back into its crystalline form.

Source: California Institute of Technology

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