Reflectance of pristine and n-doped epitaxial graphene from THz to mid-IR

Graphene optical properties were first investigated with the motivation to maximize its visibility on various substrates [1], so that graphene flakes could easily be located and then patterned to fabricate electronic devices. But a few key experiments revealed that there was much more to expect from this research area, and, today, one can already state that graphene optical properties offer perspectives for various applications in the near future [2]. Recent experiments demonstrated that a gate voltage could tune graphene reflectance and transmittance, particularly in the infrared (IR) range [3]. This tunability was found to stem from strong changes in the Drude component of the optical conductivity, particularly important in the far-IR, and from gate-induced shift of interband transitions, governed by a peculiar threshold at 2EF in graphene (where EF is the Fermi energy)