Tuesday, June 17, 2008

Plastic Diode Lasers may be on the Horizon

The light from a diode laser is created by passing an electrical current through 2 dissimilar inorganic semiconductor materials. This approach has worked well over the years, but it has been limiting in the spectrum that can be emitted.

Now scientists are looking into a material called polydioctylfluorene that may change things. It seems that most plastics cannot support the continuous electrical charge passing through them to create a laser light wavelength, but polydioctylfluorene is showing great promise. The material emits light in the blue range and is 200 more times more efficient than previous materials.

From The Imperial College of London web site:

Conventional electrically-powered laser diodes used in everyday consumer goods like DVD players are currently based on inorganic semiconductor materials such as gallium arsenide, gallium nitride and related alloys. The term 'semiconductor' describes the material’s ability to pass an electric current, which lies somewhere between that of a metallic conductor and that of an insulator.

In the case of a laser diode, the current comprises positive and negative charges that combine inside the material and produce the initial light required to begin the lasing process. If the initial light can be forced to pass back and forth through the semiconducting material many times, in a way that amplifies its strength on each pass, then after a short time a spectrally narrow, intense and directional laser beam emerges.


The last two decades have seen tremendous developments in new organic-molecule-based semiconductors, including a special class of plastics. Many important devices based on such plastics have successfully been developed, including light emitting diodes for displays and lighting, field effect transistors for electrical circuits, and photodiodes for solar energy conversion and light detection. However, despite over a decade of worldwide research, plastic laser diodes remain the only major device type not yet demonstrated.

One of the main stumbling blocks is that, until now, it was widely considered that plastic semiconductor laser diodes would be impossible to produce because scientists had not found or developed any plastics that could sustain a large enough current whilst also supporting the efficient light emission needed to produce a laser beam.

Now a team of Imperial physicists, publishing their findings in Nature Materials in April, have done just that. The plastics studied, synthesised by the Sumitomo Chemical Company in Japan, are closely related to PFO, an archetype blue-light emitting material. By making subtle changes in the plastic's chemical structure the researchers produced a material that transports charges 200 times better than before, without compromising its ability to efficiently emit light - indeed the generation of laser light was actually improved.

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