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The peculiar electronic structure of graphene results in a large optoelectronic response that holds great potential for technology. For example, this material exhibits a nearly constant absorption ~2.3% over a broad spectral range [1], which can be electrically modulated in the mid-IR by injecting attainable densities of charge carriers. When doped, graphene can sustain plasmons that radically modify its optical response, enabling complete optical absorption for suitably designed patterns [2]. Graphene nanoribbons constitute one of the simplest geometrical patterns that one can produce. They have been extensively studied and their plasmons accurately explained with simple models [3]. When heated to a large electronic temperature, graphene behaves nearly as if is was highly doped, also giving rise to plasmon modes [4].
In this work, we study the possibility of using ultrashort light pulses together with the natural electronic relaxation mechanisms in graphene nanoribbons as a way to tune their optical response. We first discuss the optically induced plasmons of individual nanoribbons when illuminated with ultrashort pulses and then analyze the evolution of the plasmon frequency as a function of the delay between pump and probe. We study the redshift of these plasmons with increasing delay due to electron relaxation. We also investigate the optical response of the ribbon exposed to a train of optical pulses. We further discuss ribbon arrays illuminated from the substrate under total internal reflection conditions, for which we predict complete absorption for a suitable choice of geometrical and illumination parameters.
References
[1] F. H. L. Koppens, D. E. Chang, and F. J. García de Abajo, Nano Letters 11, 3370-3377 (2011)
[2] S. Thongrattanasiri, F. H. L. Koppens, and F. J. García de Abajo, Phys. Rev. Lett. 108, 047401 (2012)
[3] I. Silveiro, J. M. Plaza Ortega, and F. J. García de Abajo, Light: Science and Applications 4, e241 (2015)
[4] F. J. García de Abajo, ACS Photon. 1, 135 (2014).
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