Pages- Terahertz Imaging & Detection

Thursday, September 25, 2014

Abstract-Theory of low-power ultra-broadband terahertz sideband generation in bi-layer graphene


http://www.nature.com/ncomms/2014/140924/ncomms5854/abs/ncomms5854.html
Nature Communications
 
5,
 
Article number:
 
4854
 
doi:10.1038/ncomms5854
Received
 
Accepted
 
Published
 


In a semiconductor illuminated by a strong terahertz (THz) field, optically excited electron–hole pairs can recombine to emit light in a broad frequency comb evenly spaced by twice the THz frequency. Such high-order THz sideband generation is of interest both as an example of extreme nonlinear optics and also as a method for ultrafast electro-optical modulation. So far, this phenomenon has only been observed with large field strengths (~10 kV cm−1), an obstacle for technological applications. Here we predict that bi-layer graphene generates high-order sidebands at much weaker THz fields. We find that a THz field of strength 1 kV cm−1 can produce a high-sideband spectrum of about 30 THz, 100 times broader than in ​GaAs. The sidebands are generated despite the absence of classical collisions, with the quantum coherence of the electron–hole pairs enabling recombination. These remarkable features lower the barrier to desktop electro-optical modulation at THz frequencies, facilitating ultrafast optical communications.

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