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17 Jun 2002
An erasable-rewritable optical memory that promises to store up to 5 Gbit/cm3 has been made from a photorefractive polymer.
The system, developed by researchers at the Victoria University of Technology, Australia, stores information by shining a light beam on the polymer and changing its refractive index.
Data are written and rewritten by a pulsed beam of infrared radiation at 800 nanometres that causes two-photon excitation. A microscope focuses the beam onto a small region of the polymer. The data are read by a HeNe laser and erased on exposure by ultraviolet light.
Two-photon excitation is attractive for optical storage because excitation only occurs in a small region of the focused beam. This gives a higher density of data and reduces cross-talk between neighbouring data layers.
Recording in thick samples is possible because infrared radiation penetrates the polymer deeply. The researchers have made films with a uniform thickness of up to 200 micrometres.
The material consists of the polymer poly(N-vinylcarbazole) doped with three other compounds that provide light absorption and physical stability.
This research was reported in the journal Optics Letters (24(14) 948).
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