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

ABSTRACT: 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.

SUBMITTER: Crosse JA 

PROVIDER: S-EPMC4200518 | biostudies-literature | 2014 Sep

REPOSITORIES: biostudies-literature