Scientists have harnessed the power of holography to store large amounts of data in a postage stamp-sized disc.

Craig Hawker, at the University of California, Santa Barbara, US, and colleagues designed photopolymers that can store up to 50 times more data than a DVD.

When the highly branched molecules polymerise, the volume change is negligible so data can be stored and retrieved accurately

Unlike a DVD, which only uses a disc's surface, holographic data storage uses the whole volume of the disc. As a result, holography promises terabytes (1000 gigabytes) of storage capacity in a recording disc the size of a postage stamp, says Hawker. A typical DVD holds only 4.7 gigabytes.

Recently, researchers have investigated light-sensitive polymers - which are used to make the holograms seen in driving licences - for data storage. But these photopolymers shrink as the molecules polymerise during the recording process, making it difficult to accurately retrieve the recorded data.

Hawker overcame this problem by making a series of highly branched monomers. He showed that when the molecules polymerised, the volume change was much smaller than for previous photopolymers and so the shrinkage was negligible.

'Of particular note is finding that a holographic medium prepared using one of our monomers exhibits 50 times more storage capacity than a conventional DVD,' says Hawker. 'To reach the terabyte goal, you need to have very high efficiency and fidelity during the recording process.'

The polymer's refractive index, which is a measure of how much it reduces the speed of light passing through it, is key to increased storage capacity, explains Hawker. He is working on a system that combines a low refractive index scaffold with ultra-high refractive index monomers, which he expects to show improved results.

'This work illustrates the power of modern polymer synthesis to custom-design organic materials with advantageous properties,' says Stefan Hecht, an expert in organic functional materials at Humboldt University, Berlin, Germany. 'By fine tuning the macromolecular architecture, Hawker and co-workers have created new high performance data storage materials overcoming limitations of conventional polymer chemistry.'

Sarah Corcoran

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