Breakthrough In Plastic Lasers 54
esocid writes "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. Plastic laser diodes offer the promise of covering more of the light spectrum than their counterparts, from near ultraviolet to the near infrared. Yet despite over a decade of research worldwide, plastic laser diodes have not yet been demonstrated because there haven't been any plastics that could sustain a large enough current while also supporting the efficient light emission needed to produce a laser beam. Now researchers at Imperial College London, publishing their findings in Nature Materials in April, are studying a plastic related to PFO (polydioctylfluorene), a blue-light emitting material; by making subtle changes in the plastic's chemical structure they have produced a material that transports charges 200 times better than before, while actually increasing its ability to emit light efficiently."
Original paper, and laser wavelength tunability (Score:5, Informative)
Something cool is that while traditional semiconductor lasers have an output wavelength that is very much controlled by the bandgap energy of the material, here the laser is substantially tunable by adjusting the plastic's thickness. (Of course, this is just adjusting the energy states too, but it seems more tunable.) From the paper, "Tuning the film thickness (45-160 nm) enabled access to lasing wavelengths across a 45 nm spectral window (434-479 nm)."
While it's not real-time electrical tuning over that kind of bandwidth, it's still pretty cool. Tunability is especially useful for detectors of various chemicals, and now this is getting into the wavelength range where more biological substances start to have their spectrographic signatures.
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Electronics kits for the digital generation! [nerdkits.com]
Re:What about chromatically accurate displays? (Score:5, Informative)
Pixels don't actually "change color" now. The individual pixels in your display change the relative brightness of three sub-pixel elements, but the frequency of each element emits doesn't change... the relative proportions of three fixed colors change. This is of course an approximation an approximation that is usually good enough to fool the eye, which means it's good enough for most purposes, but it's not chromatically accurate and there are applications where that matters.
Re:What about chromatically accurate displays? (Score:2, Informative)
I'm not sure why you'd want to - lasers have a narrowband emission; better would be to find some chemical structures that replicate (in bulk emission properties) the response of the sensors of the eye.
A step in the right direction (Score:4, Informative)
The holy grail is an electrically pumped organic laser. Varying the co-polymer ratios has improved electron mobilities, but they still have many orders of magnitudes to go before they would get into the likely energy densities required for lasing.
People are attacking it from multiple ends. Bradley's group have gone at it by taking an efficient light emitter and attempting to improve its pitiful charge mobilities. Others have taken very good charge carrying organic materials, LETs (light emitting transistors) and attempted to improve their pitiful light emission. (paper) [aps.org]
Re:Awsome (Score:1, Informative)
Re:What about chromatically accurate displays? (Score:4, Informative)
I don't know what you mean by changing the color "in real time", but it seems to me that you're talking about electrochemical display devices. They're ridiculously simple to build and can cover a wide range of contrasts. Granted, PEDOT:PSS or similar materials can only go from transparent to dark blue (through a lot of shades of blue), and switching time is quite slow, but let's not forget that this field is at its infancy. Hang around, organic electronics might be huge in the medium term.
Re:What about chromatically accurate displays? (Score:2, Informative)
They are directly tuneable - as a broad gain medium, you can just change the cavity to _tune_ (literally!) the frequency of light produced by varying the modes which can be supported by the cavity.
The chemistry will vary the range over which you can do this, though polyfluorene already has a nice fat response up in the blue.
This is exactly the same as an optically pumped dye laser, as often used for research in the 1980s, but these required jets of the nasty stuff getting flung around and were strictly research lab objects.
Re:Original paper, and laser wavelength tunability (Score:3, Informative)