All-optical generation of surface plasmons in graphene

Abstract

Surface plasmons in graphene o er a compelling route to many useful photonic technologies [1][2][3] . As a plasmonic material, graphene o ers several intriguing properties, such as excellent electro-optic tunability 4 , crystalline stability, large optical nonlinearities 5 and extremely high electromagnetic field concentration 6 . As such, recent demonstrations of surface plasmon excitation in graphene using near-field scattering of infrared light 7,8 have received intense interest. Here we present an all-optical plasmon coupling scheme which takes advantage of the intrinsic nonlinear optical response of graphene. Free-space, visible light pulses are used to generate surface plasmons in a planar graphene sheet using di erence frequency wave mixing to match both the wavevector and energy of the surface wave. By carefully controlling the phase matching conditions, we show that one can excite surface plasmons with a defined wavevector and direction across a large frequency range, with an estimated photon e ciency in our experiments approaching 10 −5 . Graphene has attracted significant interest recently as a unique optical material. In particular, it has been predicted and experimentally shown that graphene can support highly confined surface plasmons 1,9 , with electrically tunable dispersion 7,8 . Despite these promising discoveries, the burgeoning field of graphene plasmonics has some serious obstacles to overcome if it is to progress from the proof-of-principle stage. Problems arise due to the small wavelength of the surface plasmons, two orders of magnitude smaller than light of the same frequency. This has led to the development of specialized measurement techniques, most of which use infrared light and geometries with scattering resonances 10-12 or near-field sources 7,8 to excite graphene surface plasmons. However, the far-infrared regime, in which graphene plasmons are predicted to have long lifetimes, lacks developed sources and detectors compared to the visible regime. Alternative approaches, such as the manipulation of surface acoustic waves to couple to the graphene surface plasmons 13,14 , therefore hold promise. Particularly desirable is the potential to excite a plasmon eigenstate with a singular energy, momentum and direction, vital for many future applications, including plasmonic circuits. In this respect, very recent progress has been made, with the development of carefully designed nanoantennas which can locally excite and direct surface plasmons in graphene 11 . Here, the combination of infrared source frequency and nanoantenna dimensions determine the frequency, wavevector and direction of the surface plasmons generated. In this letter, we investigate a competing approach that embodies many of these desirable aspects of directivity without requiring careful nanofabrication of antennas. This all-optical approach can access a distinctly broad frequency range, even down to the far infrared. We coherently excite surface plasmons using two visible frequency free-space beams via difference frequenc...

Transient nonlinear plasmonics in nanostructured graphene

“…Results are presented for continuous-wave (cw) illumination, individual ultrashort pulses, and degenerate pump-probe irradiation. With only a few reported measurements on the nonlinear plasmonic response of graphene [30,34], our work elucidates the role of electronic heating and out-of-equilibrium dynamics in optical absorption associated with graphene plasmons. In particular, we show that the incoherent response due to the out-of-equilibrium electronic distribution produces a remarkable reduction in the light intensity threshold for saturable absorption that persists over hundreds of femtoseconds, as revealed by pump-probe spectroscopy simulations.…”

Modeling the excitation of graphene plasmons in periodic grids of graphene ribbons: An analytical approach

“…That foundational publication paved the way for the emergence of many experimental and theoretical works that soon followed, thereby establishing the field of graphene plasmonics [17][18][19][20][21][22][23][24]. As of today, GSPs have been realized in a number of systems, ranging from patterned grids of graphene ribbons [26,27,38,40,[48][49][50][51][52][53], disks [51,[54][55][56][57], and rings [54,55], periodic antidot lattices [57][58][59], resonators [60,61], and hybrid graphenemetal nanoantennas [43,44,[62][63][64], among others [65][66][67][68][69][70][71][72][73][74].…”

“…For extended graphene, these volumes can be about α 3 ≈ 10 −6 times smaller (where α denotes the fine-structure constant) than the volume characterized by the free-space light's wavelength (i.e., λ −3 0 ). Typical strategies to couple light to graphene plasmons involve the patterning of pristine graphene into gratings and related nanostructures [26,27,38,40,[48][49][50][51][51][52][53][54][55][56][57][57][58][59], the use of dielectric gratings [65,66], light scattering from a conductive tip [71][72][73][74], and even nonlinear three-wave mixing [69,70].…”

Nonlinear graphene plasmonics

“…This method uses two pump photons that create a plasmon at their difference frequency, as shown in figure 15. Generation efficiencies of 10 −5 have been recorded [136], and theoretical efficiencies are predicted to reach 1%.…”

“…Recently, nonlinear optical processes were also studied as a way to generate graphene plasmons. For example, the difference frequency generation (DFG) method makes use of ubiquitous visible light sources and converts them to far-infrared plasmons via graphene's ultrahigh second-order nonlinearity [135,136]. This method uses two pump photons that create a plasmon at their difference frequency, as shown in figure 15.…”