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17 Jun 2002
Polymer lasers that emit in the infrared are possible, according to predictions by physicists at the University of Arizona.
Polymer-based solid-state lasers offer a cheap alternative to semiconductor lasers because the organic precursors are low cost and can be processed from solution at low temperature rather than requiring molecular beam epitaxy techniques.
The bandgap of the polymers, and therefore the wavelength of emitted light, can easily be tuned by altering the structure slightly. Until now, most of the research in this area has focused on visible and ultraviolet light because it was believed that the optical transitions required for the emission of longer wavelengths were not possible with organic polymers.
Telecommunications systems use infrared radiation, so lasing at these wavelengths is desirable. Alok Shukla and Sumit Mazumdar have now shown that, if a new approach is taken to designing polymeric lasers, light can be emitted from small bandgaps, making an infrared polymeric laser possible.
The researchers carried out theoretical studies starting from the polymer trans-polyacetylene, which does not emit light, and modifying the chemical groups attached to the polymer, rather than changing the bonding in the polymer chain. For luminescence, excited photons must lose energy in a certain way, so alternative paths, like that provided by interactions between the electrons in the polymer, need to be avoided. The calculations showed that chemical groups with certain electronic properties can restrict the interactions of the electrons in the chain. The same groups can also give the small bandgap needed for infrared.
Mazumbar says that he will now be collaborating with experimental colleagues to make infrared lasers based on the predictions. The study was reported in the 8 November 1999 issue of Physical Review Letters.
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