Theory of graphene saturable absorption

Abstract

Saturable absorption is a non-perturbative nonlinear optical phenomenon that plays a pivotal role in the generation of ultrafast light pulses. Here we show that this effect emerges in graphene at unprecedentedly low light intensities, thus opening avenues to new nonlinear physics and applications in optical technology. Specifically, we theoretically investigate saturable absorption in extended graphene by developing a non-perturbative single-particle approach, describing conduction-electron dynamics in the atomically-thin material using the two-dimensional Dirac equation for massless Dirac fermions, which is recast in the form of generalized Bloch equations. By solving the electron dynamics non-perturbatively, we account for both interband and intraband contributions to the intensity-dependent saturated conductivity and conclude that the former dominates regardless of the intrinsic doping state of the material. The results are in excellent agreement with atomistic quantum-mechanical simulations including higher-band effects. Additionally, we find that the modulation depth of saturable absorption in graphene can be electrically manipulated through an externally applied gate voltage. Our results are relevant for the development of graphene-based optoelectronic devices, as well as for applications in mode-locking and random lasers

Strong Light–Matter Interactions Enabled by Polaritons in Atomically Thin Materials

“…HHG is one such process, predicted to be particularly effective in highly doped, nanostructured graphene due to the synergetic combination of plasmonic near‐field enhancement and anharmonic intraband charge carrier motion near the Dirac point (see Figure b). Plasmon‐assisted HHG in graphene is however competing with its strong intrinsic saturable absorption, which diminishes the in‐plane plasmonic near‐field enhancement in the material; the coherent saturable absorption is augmented by an incoherent saturation originating in the optical heating of electrons, which becomes substantial due to enhanced light absorption at the plasmon resonance …”

Transient nonlinear plasmonics in nanostructured graphene

“…However, most experimental studies on graphene nonlinear optics have dealt with interband effects, including reports of large third-order susceptibilities linked to wave mixing [18], harmonic generation [19][20][21][22][23], and the Kerr effect [24][25][26]. Carbon monolayers are also an attractive platform for passive mode locking and other applications that rely on saturable absorption, which in undoped graphene emerges at remarkably low light intensities [27,28]. Although saturable absorption can be coherently induced, particularly in few-level molecular systems, the high optical intensities required to trigger this effect invariably lead to incoherent processes that substantially alter the response of a material such as graphene.…”

Spontaneous emission in plasmonic graphene subwavelength wires of arbitrary sections

“…Significant progress made in nanoscale fabrication and an extensive wealth of theoretical analysis have allowed possible a wide range of applications based on the interaction between graphene and electromagnetic radiation via SP mechanisms, including plasmonic signal processing [10], sensing [11,12], quantum optics and nonlinear photonics [13,14].…”