Ordinarily optical switches respond at rate of a few picoseconds – around a trillionth of a second. Through this study physicists have observed the response rate of an optical switch using ‘few layer graphene’ to be around one hundred femtoseconds – nearly a hundred times quicker than current materials.
Commenting on the report’s main findings, lead researcher Dr Enrico Da Como said: “We’ve seen an ultrafast optical response rate, using ‘few-layer graphene’, which has exciting applications for the development of high speed optoelectronic components based on graphene. This fast response is in the infrared part of the electromagnetic spectrum, where many applications in telecommunications, security and also medicine are currently developing and affecting our society.”
In the long term this research could also lead to the development of quantum cascade lasers based on graphene. Quantum cascade lasers are semiconductor lasers used in pollution monitoring, security and spectroscopy. Few-layer graphene could emerge as a unique platform for this interesting application.
We report a femtosecond transient spectroscopy study in the near to middle infrared range, 0.8–0.35 eV photon energy, on graphene and few layer graphene single flakes. The spectra show an evolving structure of photoinduced absorption bands superimposed on the bleaching caused by Pauli blocking of the interband optically coupled states. Supported by tight-binding model calculations, we assign the photoinduced absorption features to intersubband transitions as the number of layers is increased. Interestingly, the intersubband photoinduced resonances show a longer dynamics than the interband bleaching, because of their independence from the absolute energy of the carriers with respect to the Dirac point. The dynamic of these intersubband transitions reflects the lifetime of the hot carriers and provides an elegant method to access it in this important class of semimetals.
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